This vignette explains briefly how
to use the function adam()
and the related
auto.adam()
in smooth
package. It does not aim
at covering all aspects of the function, but focuses on the main
ones.
ADAM is Augmented Dynamic Adaptive Model. It is a model that underlies ETS, ARIMA and regression, connecting them in a unified framework. The underlying model for ADAM is a Single Source of Error state space model, which is explained in detail separately in an online textbook.
The main philosophy of adam()
function is to be agnostic
of the provided data. This means that it will work with ts
,
msts
, zoo
, xts
,
data.frame
, numeric
and other classes of data.
The specification of seasonality in the model is done using a separate
parameter lags
, so you are not obliged to transform the
existing data to something specific, and can use it as is. If you
provide a matrix
, or a data.frame
, or a
data.table
, or any other multivariate structure, then the
function will use the first column for the response variable and the
others for the explanatory ones. One thing that is currently assumed in
the function is that the data is measured at a regular frequency. If
this is not the case, you will need to introduce missing values
manually.
In order to run the experiments in this vignette, we need to load the following packages:
First and foremost, ADAM implements ETS model, although in a more
flexible way than (Hyndman et al. 2008):
it supports different distributions for the error term, which are
regulated via distribution
parameter. By default, the
additive error model relies on Normal distribution, while the
multiplicative error one assumes Inverse Gaussian. If you want to
reproduce the classical ETS, you would need to specify
distribution="dnorm"
. Here is an example of ADAM ETS(MMM)
with Normal distribution on AirPassengers
data:
testModel <- adam(AirPassengers, "MMM", lags=c(1,12), distribution="dnorm",
h=12, holdout=TRUE)
summary(testModel)
#>
#> Model estimated using adam() function: ETS(MMM)
#> Response variable: AirPassengers
#> Distribution used in the estimation: Normal
#> Loss function type: likelihood; Loss function value: 470.6091
#> Coefficients:
#> Estimate Std. Error Lower 2.5% Upper 97.5%
#> alpha 0.6661 0.0819 0.5039 0.8278 *
#> beta 0.0038 0.0226 0.0000 0.0485
#> gamma 0.0298 0.0351 0.0000 0.0991
#> level 111.4423 5.5993 100.3511 122.5066 *
#> trend 1.0098 0.0028 1.0042 1.0154 *
#> seasonal_1 0.8973 0.0058 0.8859 0.9227 *
#> seasonal_2 0.8991 0.0096 0.8876 0.9245 *
#> seasonal_3 1.0297 0.0107 1.0182 1.0550 *
#> seasonal_4 0.9957 0.0090 0.9843 1.0211 *
#> seasonal_5 1.0021 0.0070 0.9907 1.0275 *
#> seasonal_6 1.1352 0.0093 1.1237 1.1605 *
#> seasonal_7 1.2382 0.0128 1.2268 1.2636 *
#> seasonal_8 1.2237 0.0112 1.2122 1.2490 *
#> seasonal_9 1.0642 0.0107 1.0527 1.0895 *
#> seasonal_10 0.9236 0.0096 0.9121 0.9489 *
#> seasonal_11 0.8004 0.0083 0.7889 0.8257 *
#>
#> Error standard deviation: 0.0379
#> Sample size: 132
#> Number of estimated parameters: 17
#> Number of degrees of freedom: 115
#> Information criteria:
#> AIC AICc BIC BICc
#> 975.2182 980.5866 1024.2258 1037.3323
plot(forecast(testModel,h=12,interval="prediction"))
You might notice that the summary contains more than what is reported
by other smooth
functions. This one also produces standard
errors for the estimated parameters based on Fisher Information
calculation. Note that this is computationally expensive, so if you have
a model with more than 30 variables, the calculation of standard errors
might take plenty of time. As for the default print()
method, it will produce a shorter summary from the model, without the
standard errors (similar to what es()
does):
testModel
#> Time elapsed: 0.14 seconds
#> Model estimated using adam() function: ETS(MMM)
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 470.6091
#> Persistence vector g:
#> alpha beta gamma
#> 0.6661 0.0038 0.0298
#>
#> Sample size: 132
#> Number of estimated parameters: 17
#> Number of degrees of freedom: 115
#> Information criteria:
#> AIC AICc BIC BICc
#> 975.2182 980.5866 1024.2258 1037.3323
#>
#> Forecast errors:
#> ME: -11.657; MAE: 16.154; RMSE: 22.504
#> sCE: -53.291%; Asymmetry: -70%; sMAE: 6.154%; sMSE: 0.735%
#> MASE: 0.671; RMSSE: 0.718; rMAE: 0.213; rRMSE: 0.219
Also, note that the prediction interval in case of multiplicative error models are approximate. It is advisable to use simulations instead (which is slower, but more accurate):
If you want to do the residuals diagnostics, then it is recommended
to use plot
function, something like this (you can select,
which of the plots to produce):
By default ADAM will estimate models via maximising likelihood
function. But there is also a parameter loss
, which allows
selecting from a list of already implemented loss functions (again, see
documentation for adam()
for the full list) or using a
function written by a user. Here is how to do the latter on the example
of BJsales
:
lossFunction <- function(actual, fitted, B){
return(sum(abs(actual-fitted)^3))
}
testModel <- adam(BJsales, "AAN", silent=FALSE, loss=lossFunction,
h=12, holdout=TRUE)
testModel
#> Time elapsed: 0.03 seconds
#> Model estimated using adam() function: ETS(AAN)
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: custom; Loss function value: 599.2241
#> Persistence vector g:
#> alpha beta
#> 1.0000 0.2269
#>
#> Sample size: 138
#> Number of estimated parameters: 4
#> Number of degrees of freedom: 134
#> Information criteria are unavailable for the chosen loss & distribution.
#>
#> Forecast errors:
#> ME: 3.015; MAE: 3.129; RMSE: 3.866
#> sCE: 15.918%; Asymmetry: 91.7%; sMAE: 1.376%; sMSE: 0.029%
#> MASE: 2.626; RMSSE: 2.52; rMAE: 1.009; rRMSE: 1.009
Note that you need to have parameters actual, fitted and B in the function, which correspond to the vector of actual values, vector of fitted values on each iteration and a vector of the optimised parameters.
loss
and distribution
parameters are
independent, so in the example above, we have assumed that the error
term follows Normal distribution, but we have estimated its parameters
using a non-conventional loss because we can. Some of distributions
assume that there is an additional parameter, which can either be
estimated or provided by user. These include Asymmetric Laplace
(distribution="dalaplace"
) with alpha
,
Generalised Normal and Log-Generalised normal
(distribution=c("gnorm","dlgnorm")
) with shape
and Student’s T (distribution="dt"
) with
nu
:
The model selection in ADAM ETS relies on information criteria and
works correctly only for the loss="likelihood"
. There are
several options, how to select the model, see them in the description of
the function: ?adam()
. The default one uses
branch-and-bound algorithm, similar to the one used in
es()
, but only considers additive trend models (the
multiplicative trend ones are less stable and need more attention from a
forecaster):
testModel <- adam(AirPassengers, "ZXZ", lags=c(1,12), silent=FALSE,
h=12, holdout=TRUE)
#> Forming the pool of models based on... ANN , ANA , MNM , MAM , Estimation progress: 71 %86 %100 %... Done!
testModel
#> Time elapsed: 0.69 seconds
#> Model estimated using adam() function: ETS(MAM)
#> With optimal initialisation
#> Distribution assumed in the model: Gamma
#> Loss function type: likelihood; Loss function value: 466.9086
#> Persistence vector g:
#> alpha beta gamma
#> 0.7807 0.0003 0.0002
#>
#> Sample size: 132
#> Number of estimated parameters: 17
#> Number of degrees of freedom: 115
#> Information criteria:
#> AIC AICc BIC BICc
#> 967.8172 973.1857 1016.8249 1029.9313
#>
#> Forecast errors:
#> ME: 11.859; MAE: 22.322; RMSE: 26.996
#> sCE: 54.214%; Asymmetry: 68.4%; sMAE: 8.504%; sMSE: 1.058%
#> MASE: 0.927; RMSSE: 0.862; rMAE: 0.294; rRMSE: 0.262
Note that the function produces point forecasts if
h>0
, but it won’t generate prediction interval. This is
why you need to use forecast()
method (as shown in the
first example in this vignette).
Similarly to es()
, function supports combination of
models, but it saves all the tested models in the output for a potential
reuse. Here how it works:
testModel <- adam(AirPassengers, "CXC", lags=c(1,12),
h=12, holdout=TRUE)
testForecast <- forecast(testModel,h=18,interval="semiparametric", level=c(0.9,0.95))
testForecast
#> Point forecast Lower bound (5%) Lower bound (2.5%) Upper bound (95%)
#> Jan 1960 411.7284 388.9060 384.6620 435.0953
#> Feb 1960 406.5590 377.9249 372.6446 436.0670
#> Mar 1960 466.6605 427.2715 420.0654 507.4993
#> Apr 1960 449.9171 408.8108 401.3205 492.6667
#> May 1960 450.5760 408.4541 400.7882 494.4225
#> Jun 1960 512.9144 462.9301 453.8543 565.0361
#> Jul 1960 569.9673 512.4185 501.9906 630.0703
#> Aug 1960 569.1866 510.7379 500.1577 630.2760
#> Sep 1960 498.4551 447.3865 438.1411 551.8259
#> Oct 1960 434.6231 389.7640 381.6464 481.5206
#> Nov 1960 378.8849 339.6652 332.5695 419.8925
#> Dec 1960 426.5414 381.4206 373.2682 473.7671
#> Jan 1961 433.3114 385.2139 376.5507 483.7699
#> Feb 1961 427.7775 377.6289 368.6300 480.5350
#> Mar 1961 490.9117 429.1080 418.0754 556.1836
#> Apr 1961 473.1945 410.6973 399.5832 539.3836
#> May 1961 473.7861 410.4375 399.1835 540.9272
#> Jun 1961 539.2199 466.5032 453.5946 616.3333
#> Upper bound (97.5%)
#> Jan 1960 439.7020
#> Feb 1960 441.9294
#> Mar 1960 515.6710
#> Apr 1960 501.2512
#> May 1960 503.2368
#> Jun 1960 575.5352
#> Jul 1960 642.1989
#> Aug 1960 642.6145
#> Sep 1960 562.6044
#> Oct 1960 490.9955
#> Nov 1960 428.1788
#> Dec 1960 483.3211
#> Jan 1961 494.0053
#> Feb 1961 491.2710
#> Mar 1961 569.5253
#> Apr 1961 552.9558
#> May 1961 554.7064
#> Jun 1961 632.1691
plot(testForecast)
Yes, now we support vectors for the levels in case you want to produce several. In fact, we also support side for prediction interval, so you can extract specific quantiles without a hustle:
forecast(testModel,h=18,interval="semiparametric", level=c(0.9,0.95,0.99), side="upper")
#> Point forecast Upper bound (90%) Upper bound (95%) Upper bound (99%)
#> Jan 1960 411.7284 429.8240 435.0953 445.0988
#> Feb 1960 406.5590 429.3724 436.0670 448.8109
#> Mar 1960 466.6605 498.1849 507.4993 525.2812
#> Apr 1960 449.9171 482.8908 492.6667 511.3560
#> May 1960 450.5760 484.3877 494.4225 513.6150
#> Jun 1960 512.9144 553.0895 565.0361 587.9036
#> Jul 1960 569.9673 616.2759 630.0703 656.4936
#> Aug 1960 569.1866 616.2460 630.2760 657.1600
#> Sep 1960 498.4551 539.5697 551.8259 575.3103
#> Oct 1960 434.6231 470.7477 481.5206 502.1658
#> Nov 1960 378.8849 410.4715 419.8925 437.9484
#> Dec 1960 426.5414 462.9081 473.7671 494.5886
#> Jan 1961 433.3114 472.1445 483.7699 506.0847
#> Feb 1961 427.7775 468.3510 480.5350 503.9517
#> Mar 1961 490.9117 541.0599 556.1836 585.3014
#> Apr 1961 473.1945 524.0113 539.3836 569.0174
#> May 1961 473.7861 525.3239 540.9272 571.0165
#> Jun 1961 539.2199 598.4040 616.3333 650.9165
A brand new thing in the function is the possibility to use several
frequencies (double / triple / quadruple / … seasonal models). In order
to show how it works, we will generate an artificial time series,
inspired by half-hourly electricity demand using sim.gum()
function:
ordersGUM <- c(1,1,1)
lagsGUM <- c(1,48,336)
initialGUM1 <- -25381.7
initialGUM2 <- c(23955.09, 24248.75, 24848.54, 25012.63, 24634.14, 24548.22, 24544.63, 24572.77,
24498.33, 24250.94, 24545.44, 25005.92, 26164.65, 27038.55, 28262.16, 28619.83,
28892.19, 28575.07, 28837.87, 28695.12, 28623.02, 28679.42, 28682.16, 28683.40,
28647.97, 28374.42, 28261.56, 28199.69, 28341.69, 28314.12, 28252.46, 28491.20,
28647.98, 28761.28, 28560.11, 28059.95, 27719.22, 27530.23, 27315.47, 27028.83,
26933.75, 26961.91, 27372.44, 27362.18, 27271.31, 26365.97, 25570.88, 25058.01)
initialGUM3 <- c(23920.16, 23026.43, 22812.23, 23169.52, 23332.56, 23129.27, 22941.20, 22692.40,
22607.53, 22427.79, 22227.64, 22580.72, 23871.99, 25758.34, 28092.21, 30220.46,
31786.51, 32699.80, 33225.72, 33788.82, 33892.25, 34112.97, 34231.06, 34449.53,
34423.61, 34333.93, 34085.28, 33948.46, 33791.81, 33736.17, 33536.61, 33633.48,
33798.09, 33918.13, 33871.41, 33403.75, 32706.46, 31929.96, 31400.48, 30798.24,
29958.04, 30020.36, 29822.62, 30414.88, 30100.74, 29833.49, 28302.29, 26906.72,
26378.64, 25382.11, 25108.30, 25407.07, 25469.06, 25291.89, 25054.11, 24802.21,
24681.89, 24366.97, 24134.74, 24304.08, 25253.99, 26950.23, 29080.48, 31076.33,
32453.20, 33232.81, 33661.61, 33991.21, 34017.02, 34164.47, 34398.01, 34655.21,
34746.83, 34596.60, 34396.54, 34236.31, 34153.32, 34102.62, 33970.92, 34016.13,
34237.27, 34430.08, 34379.39, 33944.06, 33154.67, 32418.62, 31781.90, 31208.69,
30662.59, 30230.67, 30062.80, 30421.11, 30710.54, 30239.27, 28949.56, 27506.96,
26891.75, 25946.24, 25599.88, 25921.47, 26023.51, 25826.29, 25548.72, 25405.78,
25210.45, 25046.38, 24759.76, 24957.54, 25815.10, 27568.98, 29765.24, 31728.25,
32987.51, 33633.74, 34021.09, 34407.19, 34464.65, 34540.67, 34644.56, 34756.59,
34743.81, 34630.05, 34506.39, 34319.61, 34110.96, 33961.19, 33876.04, 33969.95,
34220.96, 34444.66, 34474.57, 34018.83, 33307.40, 32718.90, 32115.27, 31663.53,
30903.82, 31013.83, 31025.04, 31106.81, 30681.74, 30245.70, 29055.49, 27582.68,
26974.67, 25993.83, 25701.93, 25940.87, 26098.63, 25771.85, 25468.41, 25315.74,
25131.87, 24913.15, 24641.53, 24807.15, 25760.85, 27386.39, 29570.03, 31634.00,
32911.26, 33603.94, 34020.90, 34297.65, 34308.37, 34504.71, 34586.78, 34725.81,
34765.47, 34619.92, 34478.54, 34285.00, 34071.90, 33986.48, 33756.85, 33799.37,
33987.95, 34047.32, 33924.48, 33580.82, 32905.87, 32293.86, 31670.02, 31092.57,
30639.73, 30245.42, 30281.61, 30484.33, 30349.51, 29889.23, 28570.31, 27185.55,
26521.85, 25543.84, 25187.82, 25371.59, 25410.07, 25077.67, 24741.93, 24554.62,
24427.19, 24127.21, 23887.55, 24028.40, 24981.34, 26652.32, 28808.00, 30847.09,
32304.13, 33059.02, 33562.51, 33878.96, 33976.68, 34172.61, 34274.50, 34328.71,
34370.12, 34095.69, 33797.46, 33522.96, 33169.94, 32883.32, 32586.24, 32380.84,
32425.30, 32532.69, 32444.24, 32132.49, 31582.39, 30926.58, 30347.73, 29518.04,
29070.95, 28586.20, 28416.94, 28598.76, 28529.75, 28424.68, 27588.76, 26604.13,
26101.63, 25003.82, 24576.66, 24634.66, 24586.21, 24224.92, 23858.42, 23577.32,
23272.28, 22772.00, 22215.13, 21987.29, 21948.95, 22310.79, 22853.79, 24226.06,
25772.55, 27266.27, 28045.65, 28606.14, 28793.51, 28755.83, 28613.74, 28376.47,
27900.76, 27682.75, 27089.10, 26481.80, 26062.94, 25717.46, 25500.27, 25171.05,
25223.12, 25634.63, 26306.31, 26822.46, 26787.57, 26571.18, 26405.21, 26148.41,
25704.47, 25473.10, 25265.97, 26006.94, 26408.68, 26592.04, 26224.64, 25407.27,
25090.35, 23930.21, 23534.13, 23585.75, 23556.93, 23230.25, 22880.24, 22525.52,
22236.71, 21715.08, 21051.17, 20689.40, 20099.18, 19939.71, 19722.69, 20421.58,
21542.03, 22962.69, 23848.69, 24958.84, 25938.72, 26316.56, 26742.61, 26990.79,
27116.94, 27168.78, 26464.41, 25703.23, 25103.56, 24891.27, 24715.27, 24436.51,
24327.31, 24473.02, 24893.89, 25304.13, 25591.77, 25653.00, 25897.55, 25859.32,
25918.32, 25984.63, 26232.01, 26810.86, 27209.70, 26863.50, 25734.54, 24456.96)
y <- sim.gum(orders=ordersGUM, lags=lagsGUM, nsim=1, frequency=336, obs=3360,
measurement=rep(1,3), transition=diag(3), persistence=c(0.045,0.162,0.375),
initial=cbind(initialGUM1,initialGUM2,initialGUM3))$data
We can then apply ADAM to this data:
testModel <- adam(y, "MMdM", lags=c(1,48,336), initial="backcasting",
silent=FALSE, h=336, holdout=TRUE)
testModel
#> Time elapsed: 0.97 seconds
#> Model estimated using adam() function: ETS(MMdM)[48, 336]
#> With backcasting initialisation
#> Distribution assumed in the model: Gamma
#> Loss function type: likelihood; Loss function value: 19589.51
#> Persistence vector g:
#> alpha beta gamma1 gamma2
#> 0.0373 0.0000 0.0753 0.2196
#> Damping parameter: 0
#> Sample size: 3024
#> Number of estimated parameters: 6
#> Number of degrees of freedom: 3018
#> Information criteria:
#> AIC AICc BIC BICc
#> 39191.02 39191.05 39227.11 39227.22
#>
#> Forecast errors:
#> ME: -27.774; MAE: 145.766; RMSE: 180.439
#> sCE: -30.379%; Asymmetry: -17.7%; sMAE: 0.475%; sMSE: 0.003%
#> MASE: 0.198; RMSSE: 0.176; rMAE: 0.022; rRMSE: 0.023
Note that the more lags you have, the more initial seasonal
components the function will need to estimate, which is a difficult
task. This is why we used initial="backcasting"
in the
example above - this speeds up the estimation by reducing the number of
parameters to estimate. Still, the optimiser might not get close to the
optimal value, so we can help it. First, we can give more time for the
calculation, increasing the number of iterations via
maxeval
(the default value is 40 iterations for each
estimated parameter, e.g. 40 × 5 = 200
in our case):
testModel <- adam(y, "MMdM", lags=c(1,48,336), initial="backcasting",
silent=FALSE, h=336, holdout=TRUE, maxeval=10000)
testModel
#> Time elapsed: 1.64 seconds
#> Model estimated using adam() function: ETS(MMdM)[48, 336]
#> With backcasting initialisation
#> Distribution assumed in the model: Gamma
#> Loss function type: likelihood; Loss function value: 19530.71
#> Persistence vector g:
#> alpha beta gamma1 gamma2
#> 0.0315 0.0000 0.1647 0.2333
#> Damping parameter: 0
#> Sample size: 3024
#> Number of estimated parameters: 6
#> Number of degrees of freedom: 3018
#> Information criteria:
#> AIC AICc BIC BICc
#> 39073.41 39073.44 39109.50 39109.61
#>
#> Forecast errors:
#> ME: -35.704; MAE: 140.074; RMSE: 174.306
#> sCE: -39.053%; Asymmetry: -24%; sMAE: 0.456%; sMSE: 0.003%
#> MASE: 0.19; RMSSE: 0.17; rMAE: 0.022; rRMSE: 0.022
This will take more time, but will typically lead to more refined
parameters. You can control other parameters of the optimiser as well,
such as algorithm
, xtol_rel
,
print_level
and others, which are explained in the
documentation for nloptr
function from nloptr package (run
nloptr.print.options()
for details). Second, we can give a
different set of initial parameters for the optimiser, have a look at
what the function saves:
and use this as a starting point for the reestimation (e.g. with a different algorithm):
testModel <- adam(y, "MMdM", lags=c(1,48,336), initial="backcasting",
silent=FALSE, h=336, holdout=TRUE, B=testModel$B)
testModel
#> Time elapsed: 0.43 seconds
#> Model estimated using adam() function: ETS(MMdM)[48, 336]
#> With backcasting initialisation
#> Distribution assumed in the model: Gamma
#> Loss function type: likelihood; Loss function value: 19530.71
#> Persistence vector g:
#> alpha beta gamma1 gamma2
#> 0.0315 0.0000 0.1647 0.2330
#> Damping parameter: 0.1209
#> Sample size: 3024
#> Number of estimated parameters: 6
#> Number of degrees of freedom: 3018
#> Information criteria:
#> AIC AICc BIC BICc
#> 39073.41 39073.44 39109.50 39109.61
#>
#> Forecast errors:
#> ME: -35.74; MAE: 140.081; RMSE: 174.317
#> sCE: -39.093%; Asymmetry: -24%; sMAE: 0.456%; sMSE: 0.003%
#> MASE: 0.19; RMSSE: 0.17; rMAE: 0.022; rRMSE: 0.022
If you are ready to wait, you can change the initialisation to the
initial="optimal"
, which in our case will take much more
time because of the number of estimated parameters - 389 for the chosen
model. The estimation process in this case might take 20 - 30 times more
than in the example above.
In addition, you can specify some parts of the initial state vector or some parts of the persistence vector, here is an example:
testModel <- adam(y, "MMdM", lags=c(1,48,336), initial="backcasting",
silent=TRUE, h=336, holdout=TRUE, persistence=list(beta=0.1))
testModel
#> Time elapsed: 0.64 seconds
#> Model estimated using adam() function: ETS(MMdM)[48, 336]
#> With backcasting initialisation
#> Distribution assumed in the model: Gamma
#> Loss function type: likelihood; Loss function value: 19806.28
#> Persistence vector g:
#> alpha beta gamma1 gamma2
#> 0.1024 0.1000 0.1641 0.6797
#> Damping parameter: 0
#> Sample size: 3024
#> Number of estimated parameters: 5
#> Number of degrees of freedom: 3019
#> Information criteria:
#> AIC AICc BIC BICc
#> 39622.56 39622.58 39652.63 39652.71
#>
#> Forecast errors:
#> ME: -16.687; MAE: 148.315; RMSE: 183.178
#> sCE: -18.252%; Asymmetry: -14.4%; sMAE: 0.483%; sMSE: 0.004%
#> MASE: 0.201; RMSSE: 0.179; rMAE: 0.023; rRMSE: 0.023
The function also handles intermittent data (the data with zeroes) and the data with missing values. This is partially covered in the vignette on the oes() function. Here is a simple example:
testModel <- adam(rpois(120,0.5), "MNN", silent=FALSE, h=12, holdout=TRUE,
occurrence="odds-ratio")
testModel
#> Time elapsed: 0.03 seconds
#> Model estimated using adam() function: iETS(MNN)[O]
#> With optimal initialisation
#> Occurrence model type: Odds ratio
#> Distribution assumed in the model: Mixture of Bernoulli and Gamma
#> Loss function type: likelihood; Loss function value: 71.5689
#> Persistence vector g:
#> alpha
#> 0
#>
#> Sample size: 108
#> Number of estimated parameters: 5
#> Number of degrees of freedom: 103
#> Information criteria:
#> AIC AICc BIC BICc
#> 302.5240 302.7548 315.9347 307.1106
#>
#> Forecast errors:
#> Asymmetry: -39.502%; sMSE: 33.879%; rRMSE: 0.861; sPIS: -105.448%; sCE: -165.995%
Finally, adam()
is faster than es()
function, because its code is more efficient and it uses a different
optimisation algorithm with more finely tuned parameters by default.
Let’s compare:
adamModel <- adam(AirPassengers, "CCC",
h=12, holdout=TRUE)
esModel <- es(AirPassengers, "CCC",
h=12, holdout=TRUE)
"adam:"
#> [1] "adam:"
adamModel
#> Time elapsed: 2.39 seconds
#> Model estimated: ETS(CCC)
#> Loss function type: likelihood
#>
#> Number of models combined: 30
#> Sample size: 132
#> Average number of estimated parameters: 18.0026
#> Average number of degrees of freedom: 113.9974
#>
#> Forecast errors:
#> ME: 11.488; MAE: 22.026; RMSE: 26.785
#> sCE: 52.518%; sMAE: 8.391%; sMSE: 1.041%
#> MASE: 0.915; RMSSE: 0.855; rMAE: 0.29; rRMSE: 0.26
"es():"
#> [1] "es():"
esModel
#> Time elapsed: 2.27 seconds
#> Model estimated: ETS(CCC)
#> Loss function type: likelihood
#>
#> Number of models combined: 30
#> Sample size: 132
#> Average number of estimated parameters: 18.0462
#> Average number of degrees of freedom: 113.9538
#>
#> Forecast errors:
#> ME: 1.919; MAE: 16.001; RMSE: 22.328
#> sCE: 8.773%; sMAE: 6.096%; sMSE: 0.724%
#> MASE: 0.664; RMSSE: 0.713; rMAE: 0.211; rRMSE: 0.217
As mentioned above, ADAM does not only contain ETS, it also contains
ARIMA model, which is regulated via orders
parameter. If
you want to have a pure ARIMA, you need to switch off ETS, which is done
via model="NNN"
:
testModel <- adam(BJsales, "NNN", silent=FALSE, orders=c(0,2,2),
h=12, holdout=TRUE)
testModel
#> Time elapsed: 0.06 seconds
#> Model estimated using adam() function: ARIMA(0,2,2)
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 240.5926
#> ARMA parameters of the model:
#> Lag 1
#> MA(1) -0.7483
#> MA(2) -0.0150
#>
#> Sample size: 138
#> Number of estimated parameters: 5
#> Number of degrees of freedom: 133
#> Information criteria:
#> AIC AICc BIC BICc
#> 491.1852 491.6397 505.8214 506.9413
#>
#> Forecast errors:
#> ME: 2.959; MAE: 3.085; RMSE: 3.809
#> sCE: 15.619%; Asymmetry: 90.1%; sMAE: 1.357%; sMSE: 0.028%
#> MASE: 2.589; RMSSE: 2.483; rMAE: 0.995; rRMSE: 0.994
Given that both models are implemented in the same framework, they can be compared using information criteria.
The functionality of ADAM ARIMA is similar to the one of
msarima
function in smooth
package, although
there are several differences.
First, changing the distribution
parameter will allow
switching between additive / multiplicative models. For example,
distribution="dlnorm"
will create an ARIMA, equivalent to
the one on logarithms of the data:
testModel <- adam(AirPassengers, "NNN", silent=FALSE, lags=c(1,12),
orders=list(ar=c(1,1),i=c(1,1),ma=c(2,2)), distribution="dlnorm",
h=12, holdout=TRUE)
testModel
#> Time elapsed: 0.58 seconds
#> Model estimated using adam() function: SARIMA(1,1,2)[1](1,1,2)[12]
#> With optimal initialisation
#> Distribution assumed in the model: Log-Normal
#> Loss function type: likelihood; Loss function value: 463.8379
#> ARMA parameters of the model:
#> Lag 1 Lag 12
#> AR(1) -0.775 -0.6012
#> Lag 1 Lag 12
#> MA(1) 0.3353 0.2309
#> MA(2) -0.2053 -0.2530
#>
#> Sample size: 132
#> Number of estimated parameters: 33
#> Number of degrees of freedom: 99
#> Information criteria:
#> AIC AICc BIC BICc
#> 993.6758 1016.5737 1088.8082 1144.7113
#>
#> Forecast errors:
#> ME: -17.97; MAE: 18.5; RMSE: 23.208
#> sCE: -82.15%; Asymmetry: -95.1%; sMAE: 7.048%; sMSE: 0.782%
#> MASE: 0.768; RMSSE: 0.741; rMAE: 0.243; rRMSE: 0.225
Second, if you want the model with intercept / drift, you can do it
using constant
parameter:
testModel <- adam(AirPassengers, "NNN", silent=FALSE, lags=c(1,12), constant=TRUE,
orders=list(ar=c(1,1),i=c(1,1),ma=c(2,2)), distribution="dnorm",
h=12, holdout=TRUE)
testModel
#> Time elapsed: 0.49 seconds
#> Model estimated using adam() function: SARIMA(1,1,2)[1](1,1,2)[12] with drift
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 489.6563
#> Intercept/Drift value: 0.4986
#> ARMA parameters of the model:
#> Lag 1 Lag 12
#> AR(1) -0.8542 -0.3225
#> Lag 1 Lag 12
#> MA(1) 0.5112 0.2626
#> MA(2) -0.3057 0.1392
#>
#> Sample size: 132
#> Number of estimated parameters: 34
#> Number of degrees of freedom: 98
#> Information criteria:
#> AIC AICc BIC BICc
#> 1047.312 1071.849 1145.328 1205.230
#>
#> Forecast errors:
#> ME: -9.808; MAE: 14.792; RMSE: 19.051
#> sCE: -44.837%; Asymmetry: -65.6%; sMAE: 5.635%; sMSE: 0.527%
#> MASE: 0.614; RMSSE: 0.608; rMAE: 0.195; rRMSE: 0.185
If the model contains non-zero differences, then the constant acts as
a drift. Third, you can specify parameters of ARIMA via the
arma
parameter in the following manner:
testModel <- adam(AirPassengers, "NNN", silent=FALSE, lags=c(1,12),
orders=list(ar=c(1,1),i=c(1,1),ma=c(2,2)), distribution="dnorm",
arma=list(ar=c(0.1,0.1), ma=c(-0.96, 0.03, -0.12, 0.03)),
h=12, holdout=TRUE)
testModel
#> Time elapsed: 0.2 seconds
#> Model estimated using adam() function: SARIMA(1,1,2)[1](1,1,2)[12]
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 534.8602
#> ARMA parameters of the model:
#> Lag 1 Lag 12
#> AR(1) 0.1 0.1
#> Lag 1 Lag 12
#> MA(1) -0.96 -0.12
#> MA(2) 0.03 0.03
#>
#> Sample size: 132
#> Number of estimated parameters: 27
#> Number of degrees of freedom: 105
#> Information criteria:
#> AIC AICc BIC BICc
#> 1123.720 1138.259 1201.556 1237.050
#>
#> Forecast errors:
#> ME: 9.575; MAE: 17.082; RMSE: 19.148
#> sCE: 43.773%; Asymmetry: 61.9%; sMAE: 6.508%; sMSE: 0.532%
#> MASE: 0.709; RMSSE: 0.611; rMAE: 0.225; rRMSE: 0.186
Finally, the initials for the states can also be provided, although
getting the correct ones might be a challenging task (you also need to
know how many of them to provide; checking
testModel$initial
might help):
testModel <- adam(AirPassengers, "NNN", silent=FALSE, lags=c(1,12),
orders=list(ar=c(1,1),i=c(1,1),ma=c(2,0)), distribution="dnorm",
initial=list(arima=AirPassengers[1:24]),
h=12, holdout=TRUE)
testModel
#> Time elapsed: 0.4 seconds
#> Model estimated using adam() function: SARIMA(1,1,2)[1](1,1,0)[12]
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 489.0635
#> ARMA parameters of the model:
#> Lag 1 Lag 12
#> AR(1) -0.4129 -0.1071
#> Lag 1
#> MA(1) 0.2143
#> MA(2) 0.0565
#>
#> Sample size: 132
#> Number of estimated parameters: 31
#> Number of degrees of freedom: 101
#> Information criteria:
#> AIC AICc BIC BICc
#> 1040.127 1059.967 1129.494 1177.931
#>
#> Forecast errors:
#> ME: -13.907; MAE: 16.641; RMSE: 21.651
#> sCE: -63.574%; Asymmetry: -81.5%; sMAE: 6.34%; sMSE: 0.68%
#> MASE: 0.691; RMSSE: 0.691; rMAE: 0.219; rRMSE: 0.21
If you work with ADAM ARIMA model, then there is no such thing as
“usual” bounds for the parameters, so the function will use the
bounds="admissible"
, checking the AR / MA polynomials in
order to make sure that the model is stationary and invertible (aka
stable).
Similarly to ETS, you can use different distributions and losses for
the estimation. Note that the order selection for ARIMA is done
in auto.adam()
function, not in the
adam()
! However, if you do
orders=list(..., select=TRUE)
in adam()
, it
will call auto.adam()
and do the selection.
Finally, ARIMA is typically slower than ETS, mainly because its
initial states are more difficult to estimate due to an increased
complexity of the model. If you want to speed things up, use
initial="backcasting"
and reduce the number of iterations
via maxeval
parameter.
Another important feature of ADAM is introduction of explanatory
variables. Unlike in es()
, adam()
expects a
matrix for data
and can work with a formula. If the latter
is not provided, then it will use all explanatory variables. Here is a
brief example:
If you work with data.frame or similar structures, then you can use
them directly, ADAM will extract the response variable either assuming
that it is in the first column or from the provided formula (if you
specify one via formula
parameter). Here is an example,
where we create a matrix with lags and leads of an explanatory
variable:
BJData <- cbind(as.data.frame(BJsales),as.data.frame(xregExpander(BJsales.lead,c(-7:7))))
colnames(BJData)[1] <- "y"
testModel <- adam(BJData, "ANN", h=18, silent=FALSE, holdout=TRUE, formula=y~xLag1+xLag2+xLag3)
testModel
#> Time elapsed: 0.12 seconds
#> Model estimated using adam() function: ETSX(ANN)
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 197.1386
#> Persistence vector g (excluding xreg):
#> alpha
#> 1
#>
#> Sample size: 132
#> Number of estimated parameters: 6
#> Number of degrees of freedom: 126
#> Information criteria:
#> AIC AICc BIC BICc
#> 406.2773 406.9493 423.5741 425.2147
#>
#> Forecast errors:
#> ME: 1.181; MAE: 1.618; RMSE: 2.247
#> sCE: 9.409%; Asymmetry: 50.7%; sMAE: 0.716%; sMSE: 0.01%
#> MASE: 1.326; RMSSE: 1.438; rMAE: 0.723; rRMSE: 0.895
Similarly to es()
, there is a support for variables
selection, but via the regressors
parameter instead of
xregDo
, which will then use stepwise()
function from greybox
package on the residuals of the
model:
The same functionality is supported with ARIMA, so you can have, for example, ARIMAX(0,1,1), which is equivalent to ETSX(A,N,N):
testModel <- adam(BJData, "NNN", h=18, silent=FALSE, holdout=TRUE, regressors="select", orders=c(0,1,1))
The two models might differ because they have different initialisation in the optimiser and different bounds for parameters (ARIMA relies on invertibility condition, while ETS does the usual (0,1) bounds by default). It is possible to make them identical if the number of iterations is increased and the initial parameters are the same. Here is an example of what happens, when the two models have exactly the same parameters:
BJData <- BJData[,c("y",names(testModel$initial$xreg))];
testModel <- adam(BJData, "NNN", h=18, silent=TRUE, holdout=TRUE, orders=c(0,1,1),
initial=testModel$initial, arma=testModel$arma)
testModel
#> Time elapsed: 0 seconds
#> Model estimated using adam() function: ARIMAX(0,1,1)
#> With provided initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 513.2029
#> ARMA parameters of the model:
#> Lag 1
#> MA(1) 0.2402
#>
#> Sample size: 132
#> Number of estimated parameters: 1
#> Number of degrees of freedom: 131
#> Information criteria:
#> AIC AICc BIC BICc
#> 1028.406 1028.437 1031.289 1031.364
#>
#> Forecast errors:
#> ME: 0.636; MAE: 0.636; RMSE: 0.872
#> sCE: 5.063%; Asymmetry: 100%; sMAE: 0.281%; sMSE: 0.001%
#> MASE: 0.521; RMSSE: 0.558; rMAE: 0.284; rRMSE: 0.347
names(testModel$initial)[1] <- names(testModel$initial)[[1]] <- "level"
testModel2 <- adam(BJData, "ANN", h=18, silent=TRUE, holdout=TRUE,
initial=testModel$initial, persistence=testModel$arma$ma+1)
testModel2
#> Time elapsed: 0 seconds
#> Model estimated using adam() function: ETSX(ANN)
#> With provided initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 1e+300
#> Persistence vector g (excluding xreg):
#> alpha
#> 1.2402
#>
#> Sample size: 132
#> Number of estimated parameters: 1
#> Number of degrees of freedom: 131
#> Information criteria:
#> AIC AICc BIC BICc
#> 1028.406 1028.437 1031.289 1031.364
#>
#> Forecast errors:
#> ME: 0.636; MAE: 0.636; RMSE: 0.872
#> sCE: 5.063%; Asymmetry: 100%; sMAE: 0.281%; sMSE: 0.001%
#> MASE: 0.521; RMSSE: 0.558; rMAE: 0.284; rRMSE: 0.347
Another feature of ADAM is the time varying parameters in the SSOE
framework, which can be switched on via
regressors="adapt"
:
testModel <- adam(BJData, "ANN", h=18, silent=FALSE, holdout=TRUE, regressors="adapt")
testModel$persistence
#> alpha delta1 delta2 delta3 delta4 delta5
#> 0.0004758253 0.3163533479 0.3151916749 0.3287991713 0.0026271472 0.3901947312
Note that the default number of iterations might not be sufficient in
order to get close to the optimum of the function, so setting
maxeval
to something bigger might help. If you want to
explore, why the optimisation stopped, you can provide
print_level=41
parameter to the function, and it will print
out the report from the optimiser. In the end, the default parameters
are tuned in order to give a reasonable solution, but given the
complexity of the model, they might not guarantee to give the best one
all the time.
Finally, you can produce a mixture of ETS, ARIMA and regression, by using the respective parameters, like this:
testModel <- adam(BJData, "AAN", h=18, silent=FALSE, holdout=TRUE, orders=c(1,0,0))
summary(testModel)
#>
#> Model estimated using adam() function: ETSX(AAN)+ARIMA(1,0,0)
#> Response variable: y
#> Distribution used in the estimation: Normal
#> Loss function type: likelihood; Loss function value: 48.844
#> Coefficients:
#> Estimate Std. Error Lower 2.5% Upper 97.5%
#> alpha 0.9979 0.1074 0.7852 1.0000 *
#> beta 0.2843 0.0800 0.1260 0.4424 *
#> phi1[1] -0.1329 0.0290 -0.1902 -0.0756 *
#> level 85.4714 5.2323 75.1118 95.8134 *
#> trend -0.0333 0.2609 -0.5498 0.4823
#> ARIMAState1 2.5778 6.6721 -10.6325 15.7658
#> xLag3 4.6433 0.1083 4.4289 4.8574 *
#> xLag7 0.4525 0.1194 0.2161 0.6884 *
#> xLag4 3.2369 0.1346 2.9705 3.5029 *
#> xLag6 1.1217 0.1439 0.8367 1.4062 *
#> xLag5 1.9471 0.1522 1.6458 2.2480 *
#>
#> Error standard deviation: 0.3674
#> Sample size: 132
#> Number of estimated parameters: 12
#> Number of degrees of freedom: 120
#> Information criteria:
#> AIC AICc BIC BICc
#> 121.6880 124.3098 156.2816 162.6826
This might be handy, when you explore a high frequency data, want to add calendar events, apply ETS and add AR/MA errors to it.
Finally, if you estimate ETSX or ARIMAX model and want to speed
things up, it is recommended to use initial="backcasting"
,
which will then initialise dynamic part of the model via backcasting and
use optimisation for the parameters of the explanatory variables:
testModel <- adam(BJData, "AAN", h=18, silent=TRUE, holdout=TRUE, initial="backcasting")
summary(testModel)
#>
#> Model estimated using adam() function: ETSX(AAN)
#> Response variable: y
#> Distribution used in the estimation: Normal
#> Loss function type: likelihood; Loss function value: 46.8982
#> Coefficients:
#> Estimate Std. Error Lower 2.5% Upper 97.5%
#> alpha 0.7692 0.0940 0.5831 0.9551 *
#> beta 0.4800 0.2973 0.0000 0.7692
#> xLag3 4.5775 2.6406 -0.6491 9.7981
#> xLag7 0.4197 2.6482 -4.8219 5.6555
#> xLag4 3.1574 2.3485 -1.4909 7.8005
#> xLag6 1.0822 2.3468 -3.5627 5.7220
#> xLag5 1.8379 2.2317 -2.5793 6.2501
#>
#> Error standard deviation: 0.3562
#> Sample size: 132
#> Number of estimated parameters: 8
#> Number of degrees of freedom: 124
#> Information criteria:
#> AIC AICc BIC BICc
#> 109.7964 110.9671 132.8588 135.7170
While the original adam()
function allows selecting ETS
components and explanatory variables, it does not allow selecting the
most suitable distribution and / or ARIMA components. This is what
auto.adam()
function is for.
In order to do the selection of the most appropriate distribution, you need to provide a vector of those that you want to check:
testModel <- auto.adam(BJsales, "XXX", silent=FALSE,
distribution=c("dnorm","dlaplace","ds"),
h=12, holdout=TRUE)
#> Evaluating models with different distributions... dnorm , Selecting ARIMA orders...
#> Selecting differences...
#> Selecting ARMA... |
#> The best ARIMA is selected. dlaplace , Selecting ARIMA orders...
#> Selecting differences...
#> Selecting ARMA... |
#> The best ARIMA is selected. ds , Selecting ARIMA orders...
#> Selecting differences...
#> Selecting ARMA... |-
#> The best ARIMA is selected. Done!
testModel
#> Time elapsed: 0.55 seconds
#> Model estimated using auto.adam() function: ETS(AAdN) with drift
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 236.8501
#> Intercept/Drift value: 0.6397
#> Persistence vector g:
#> alpha beta
#> 0.9550 0.2839
#> Damping parameter: 0.8551
#> Sample size: 138
#> Number of estimated parameters: 7
#> Number of degrees of freedom: 131
#> Information criteria:
#> AIC AICc BIC BICc
#> 487.7002 488.5617 508.1910 510.3135
#>
#> Forecast errors:
#> ME: 0.297; MAE: 1.051; RMSE: 1.323
#> sCE: 1.57%; Asymmetry: 8.8%; sMAE: 0.462%; sMSE: 0.003%
#> MASE: 0.882; RMSSE: 0.862; rMAE: 0.339; rRMSE: 0.345
This process can also be done in parallel on either the automatically
selected number of cores (e.g. parallel=TRUE
) or on the
specified by user (e.g. parallel=4
):
If you want to add ARIMA or regression components, you can do it in
the exactly the same way as for the adam()
function. Here
is an example of ETS+ARIMA:
testModel <- auto.adam(BJsales, "AAN", orders=list(ar=2,i=0,ma=0), silent=TRUE,
distribution=c("dnorm","dlaplace","ds","dgnorm"),
h=12, holdout=TRUE)
testModel
#> Time elapsed: 0.42 seconds
#> Model estimated using auto.adam() function: ETS(AAN)+ARIMA(2,0,0)
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 240.5239
#> Persistence vector g:
#> alpha beta
#> 0.2789 0.2134
#>
#> ARMA parameters of the model:
#> Lag 1
#> AR(1) 0.7589
#> AR(2) 0.2321
#>
#> Sample size: 138
#> Number of estimated parameters: 9
#> Number of degrees of freedom: 129
#> Information criteria:
#> AIC AICc BIC BICc
#> 499.0478 500.4540 525.3930 528.8575
#>
#> Forecast errors:
#> ME: 2.999; MAE: 3.119; RMSE: 3.858
#> sCE: 15.832%; Asymmetry: 90.6%; sMAE: 1.372%; sMSE: 0.029%
#> MASE: 2.618; RMSSE: 2.515; rMAE: 1.006; rRMSE: 1.007
However, this way the function will just use ARIMA(2,0,0) and fit it
together with ETS(A,A,N). If you want it to select the most appropriate
ARIMA orders from the provided (e.g. up to AR(2), I(1) and MA(2)), you
need to add parameter select=TRUE
to the list in
orders
:
testModel <- auto.adam(BJsales, "XXN", orders=list(ar=2,i=2,ma=2,select=TRUE),
distribution="default", silent=FALSE,
h=12, holdout=TRUE)
#> Evaluating models with different distributions... default , Selecting ARIMA orders...
#> Selecting differences...
#> Selecting ARMA... |
#> The best ARIMA is selected. Done!
testModel
#> Time elapsed: 0.16 seconds
#> Model estimated using auto.adam() function: ETS(AAdN) with drift
#> With optimal initialisation
#> Distribution assumed in the model: Normal
#> Loss function type: likelihood; Loss function value: 236.8501
#> Intercept/Drift value: 0.6397
#> Persistence vector g:
#> alpha beta
#> 0.9550 0.2839
#> Damping parameter: 0.8551
#> Sample size: 138
#> Number of estimated parameters: 7
#> Number of degrees of freedom: 131
#> Information criteria:
#> AIC AICc BIC BICc
#> 487.7002 488.5617 508.1910 510.3135
#>
#> Forecast errors:
#> ME: 0.297; MAE: 1.051; RMSE: 1.323
#> sCE: 1.57%; Asymmetry: 8.8%; sMAE: 0.462%; sMSE: 0.003%
#> MASE: 0.882; RMSSE: 0.862; rMAE: 0.339; rRMSE: 0.345
Knowing how to work with adam()
, you can use similar
principles, when dealing with auto.adam()
. Just keep in
mind that the provided persistence
, phi
,
initial
, arma
and B
won’t work,
because this contradicts the idea of the model selection.
Finally, there is also the mechanism of automatic outliers detection,
which extracts residuals from the best model, flags observations that
lie outside the prediction interval of the width level
in
sample and then refits auto.adam()
with the dummy variables
for the outliers. Here how it works:
testModel <- auto.adam(AirPassengers, "PPP", silent=FALSE, outliers="use",
distribution="default",
h=12, holdout=TRUE)
#> Evaluating models with different distributions... default , Selecting ARIMA orders...
#> Selecting differences...
#> Selecting ARMA... |--
#> The best ARIMA is selected.
#> Dealing with outliers...
testModel
#> Time elapsed: 6.02 seconds
#> Model estimated using auto.adam() function: ETSX(MMdM)
#> With optimal initialisation
#> Distribution assumed in the model: Gamma
#> Loss function type: likelihood; Loss function value: 463.744
#> Persistence vector g (excluding xreg):
#> alpha beta gamma
#> 0.7578 0.0001 0.0338
#> Damping parameter: 0.9968
#> Sample size: 132
#> Number of estimated parameters: 19
#> Number of degrees of freedom: 113
#> Information criteria:
#> AIC AICc BIC BICc
#> 965.4881 972.2738 1020.2613 1036.8280
#>
#> Forecast errors:
#> ME: -3.732; MAE: 15.105; RMSE: 21.797
#> sCE: -17.059%; Asymmetry: -14.2%; sMAE: 5.754%; sMSE: 0.69%
#> MASE: 0.627; RMSSE: 0.696; rMAE: 0.199; rRMSE: 0.212
If you specify outliers="select"
, the function will
create leads and lags 1 of the outliers and then select the most
appropriate ones via the regressors
parameter of adam.
If you want to know more about ADAM, you are welcome to visit the online textbook (this is a work in progress at the moment).