# cvloss

## Description

returns
the loss (mean squared error) obtained by the cross-validated direct forecasting model
`L`

= cvloss(`CVMdl`

)`CVMdl`

at each step of the horizon (`CVMdl.Horizon`

).
For each partition window in `CVMdl.Partition`

and each horizon step, the
function computes the loss for the test observations using a model trained on the training
observations. `CVMdl.X`

and `CVMdl.Y`

contain all
observations.

specifies additional options using one or more name-value arguments. For example, you can
specify a custom loss function.`L`

= cvloss(`CVMdl`

,`Name=Value`

)

## Examples

### Evaluate Model Using Expanding Window Cross-Validation

Create a cross-validated direct forecasting model using expanding window cross-validation. To evaluate the performance of the model:

Compute the mean squared error (MSE) on each test set using the

`cvloss`

object function.For each test set, compare the true response values to the predicted response values using the

`cvpredict`

object function.

Load the sample file `TemperatureData.csv`

, which contains average daily temperature from January 2015 through July 2016. Read the file into a table. Observe the first eight observations in the table.

```
Tbl = readtable("TemperatureData.csv");
head(Tbl)
```

Year Month Day TemperatureF ____ ___________ ___ ____________ 2015 {'January'} 1 23 2015 {'January'} 2 31 2015 {'January'} 3 25 2015 {'January'} 4 39 2015 {'January'} 5 29 2015 {'January'} 6 12 2015 {'January'} 7 10 2015 {'January'} 8 4

Create a `datetime`

variable `t`

that contains the year, month, and day information for each observation in `Tbl`

.

numericMonth = month(datetime(Tbl.Month, ... InputFormat="MMMM",Locale="en_US")); t = datetime(Tbl.Year,numericMonth,Tbl.Day);

Plot the temperature values in `Tbl`

over time.

plot(t,Tbl.TemperatureF) xlabel("Date") ylabel("Temperature in Fahrenheit")

Create a direct forecasting model by using the data in `Tbl`

. Train the model using a bagged ensemble of trees. All three of the predictors (`Year`

, `Month`

, and `Day`

) are leading predictors because their future values are known. To create new predictors by shifting the leading predictor and response variables backward in time, specify the leading predictor lags and the response variable lags.

Mdl = directforecaster(Tbl,"TemperatureF", ... Learner="bag", ... LeadingPredictors="all",LeadingPredictorLags={0:1,0:1,0:7}, ... ResponseLags=1:7)

Mdl = DirectForecaster Horizon: 1 ResponseLags: [1 2 3 4 5 6 7] LeadingPredictors: [1 2 3] LeadingPredictorLags: {[0 1] [0 1] [0 1 2 3 4 5 6 7]} ResponseName: 'TemperatureF' PredictorNames: {'Year' 'Month' 'Day'} CategoricalPredictors: 2 Learners: {[1x1 classreg.learning.regr.CompactRegressionEnsemble]} MaxLag: 7 NumObservations: 565

`Mdl`

is a `DirectForecaster`

model object. By default, the horizon is one step ahead. That is, `Mdl`

predicts a value that is one step into the future.

Partition the time series data in `Tbl`

using an expanding window cross-validation scheme. Create three training sets and three test sets, where each test set has 100 observations. Note that each observation in `Tbl`

is in at most one test set.

CVPartition = tspartition(size(Mdl.X,1),"ExpandingWindow",3, ... TestSize=100)

CVPartition = tspartition Type: 'expanding-window' NumObservations: 565 NumTestSets: 3 TrainSize: [265 365 465] TestSize: [100 100 100] StepSize: 100

The training sets increase in size from 265 observations in the first window to 465 observations in the third window.

Create a cross-validated direct forecasting model using the partition specified in `CVPartition`

. Inspect the `Learners`

property of the resulting `CVMdl`

object.

CVMdl = crossval(Mdl,CVPartition)

CVMdl = PartitionedDirectForecaster Partition: [1x1 tspartition] Horizon: 1 ResponseLags: [1 2 3 4 5 6 7] LeadingPredictors: [1 2 3] LeadingPredictorLags: {[0 1] [0 1] [0 1 2 3 4 5 6 7]} ResponseName: 'TemperatureF' PredictorNames: {'Year' 'Month' 'Day'} CategoricalPredictors: 2 Learners: {3x1 cell} MaxLag: 7 NumObservations: 565

CVMdl.Learners

`ans=`*3×1 cell array*
{1x1 timeseries.forecaster.CompactDirectForecaster}
{1x1 timeseries.forecaster.CompactDirectForecaster}
{1x1 timeseries.forecaster.CompactDirectForecaster}

`CVMdl`

is a `PartitionedDirectForecaster`

model object. The `crossval`

function trains `CVMdl.Learners{1}`

using the observations in the first training set, `CVMdl.Learner{2}`

using the observations in the second training set, and `CVMdl.Learner{3}`

using the observations in the third training set.

Compute the average test set MSE.

averageMSE = cvloss(CVMdl)

averageMSE = 53.3480

To obtain more information, compute the MSE for each test set.

`individualMSE = cvloss(CVMdl,Mode="individual")`

`individualMSE = `*3×1*
44.1352
84.0695
31.8393

The models trained on the first and third training sets seem to perform better than the model trained on the second training set.

For each test set observation, predict the temperature value using the corresponding model in `CVMdl.Learners`

.

predictedY = cvpredict(CVMdl); predictedY(260:end,:)

`ans=`*306×1 table*
TemperatureF_Step1
__________________
NaN
NaN
NaN
NaN
NaN
NaN
50.963
57.363
57.04
60.705
59.606
58.302
58.023
61.39
67.229
61.083
⋮

Only the last 300 observations appear in any test set. For observations that do not appear in a test set, the predicted response value is `NaN`

.

For each test set, plot the true response values and the predicted response values.

tiledlayout(3,1) nexttile idx1 = test(CVPartition,1); plot(t(idx1),Tbl.TemperatureF(idx1)) hold on plot(t(idx1),predictedY.TemperatureF_Step1(idx1)) legend("True Response","Predicted Response", ... Location="eastoutside") xlabel("Date") ylabel("Temperature") title("Test Set 1") hold off nexttile idx2 = test(CVPartition,2); plot(t(idx2),Tbl.TemperatureF(idx2)) hold on plot(t(idx2),predictedY.TemperatureF_Step1(idx2)) legend("True Response","Predicted Response", ... Location="eastoutside") xlabel("Date") ylabel("Temperature") title("Test Set 2") hold off nexttile idx3 = test(CVPartition,3); plot(t(idx3),Tbl.TemperatureF(idx3)) hold on plot(t(idx3),predictedY.TemperatureF_Step1(idx3)) legend("True Response","Predicted Response", ... Location="eastoutside") xlabel("Date") ylabel("Temperature") title("Test Set 3") hold off

Overall, the cross-validated direct forecasting model is able to predict the trend in temperatures. If you are satisfied with the performance of the cross-validated model, you can use the full `DirectForecaster`

model `Mdl`

for forecasting at time steps beyond the available data.

### Evaluate Model Using Holdout Validation

Create a partitioned direct forecasting model using holdout validation. To evaluate the performance of the model:

At each horizon step, compute the root relative squared error (RRSE) on the test set using the

`cvloss`

object function.At each horizon step, compare the true response values to the predicted response values using the

`cvpredict`

object function.

Load the sample file `TemperatureData.csv`

, which contains average daily temperature from January 2015 through July 2016. Read the file into a table. Observe the first eight observations in the table.

```
Tbl = readtable("TemperatureData.csv");
head(Tbl)
```

Year Month Day TemperatureF ____ ___________ ___ ____________ 2015 {'January'} 1 23 2015 {'January'} 2 31 2015 {'January'} 3 25 2015 {'January'} 4 39 2015 {'January'} 5 29 2015 {'January'} 6 12 2015 {'January'} 7 10 2015 {'January'} 8 4

Create a `datetime`

variable `t`

that contains the year, month, and day information for each observation in `Tbl`

.

numericMonth = month(datetime(Tbl.Month, ... InputFormat="MMMM",Locale="en_US")); t = datetime(Tbl.Year,numericMonth,Tbl.Day);

Plot the temperature values in `Tbl`

over time.

plot(t,Tbl.TemperatureF) xlabel("Date") ylabel("Temperature in Fahrenheit")

Create a direct forecasting model by using the data in `Tbl`

. Specify the horizon steps as one, two, and three steps ahead. Train a model at each horizon using a bagged ensemble of trees. All three of the predictors (`Year`

, `Month`

, and `Day`

) are leading predictors because their future values are known. To create new predictors by shifting the leading predictor and response variables backward in time, specify the leading predictor lags and the response variable lags.

rng("default") Mdl = directforecaster(Tbl,"TemperatureF", ... Horizon=1:3,Learner="bag", ... LeadingPredictors="all",LeadingPredictorLags={0:1,0:1,0:7}, ... ResponseLags=1:7)

Mdl = DirectForecaster Horizon: [1 2 3] ResponseLags: [1 2 3 4 5 6 7] LeadingPredictors: [1 2 3] LeadingPredictorLags: {[0 1] [0 1] [0 1 2 3 4 5 6 7]} ResponseName: 'TemperatureF' PredictorNames: {'Year' 'Month' 'Day'} CategoricalPredictors: 2 Learners: {3x1 cell} MaxLag: 7 NumObservations: 565

`Mdl`

is a `DirectForecaster`

model object. `Mdl`

consists of three regression models: `Mdl.Learners{1}`

, which predicts one step ahead; `Mdl.Learners{2}`

, which predicts two steps ahead; and `Mdl.Learners{3}`

, which predicts three steps ahead.

Partition the time series data in `Tbl`

using a holdout validation scheme. Reserve 20% of the observations for testing.

`holdoutPartition = tspartition(size(Mdl.X,1),"Holdout",0.20)`

holdoutPartition = tspartition Type: 'holdout' NumObservations: 565 NumTestSets: 1 TrainSize: 452 TestSize: 113

The test set consists of the latest 113 observations.

Create a partitioned direct forecasting model using the partition specified in `holdoutPartition`

.

holdoutMdl = crossval(Mdl,holdoutPartition)

holdoutMdl = PartitionedDirectForecaster Partition: [1x1 tspartition] Horizon: [1 2 3] ResponseLags: [1 2 3 4 5 6 7] LeadingPredictors: [1 2 3] LeadingPredictorLags: {[0 1] [0 1] [0 1 2 3 4 5 6 7]} ResponseName: 'TemperatureF' PredictorNames: {'Year' 'Month' 'Day'} CategoricalPredictors: 2 Learners: {[1x1 timeseries.forecaster.CompactDirectForecaster]} MaxLag: 7 NumObservations: 565

`holdoutMdl`

is a `PartitionedDirectForecaster`

model object. Because `holdoutMdl`

uses holdout validation rather than a cross-validation scheme, the `Learners`

property of the object contains one `CompactDirectForecaster`

model only.

Like `Mdl`

, `holdoutMdl`

contains three regression models. The `crossval`

function trains `holdoutMdl.Learners{1}.Learners{1}`

, `holdoutMdl.Learners{1}.Learners{2}`

, and `holdoutMdl.Learners{1}.Learners{3}`

using the same training data. However, the three models use different response variables because each model predicts values for a different horizon step.

holdoutMdl.Learners{1}.Learners{1}.ResponseName

ans = 'TemperatureF_Step1'

holdoutMdl.Learners{1}.Learners{2}.ResponseName

ans = 'TemperatureF_Step2'

holdoutMdl.Learners{1}.Learners{3}.ResponseName

ans = 'TemperatureF_Step3'

Compute the root relative squared error (RRSE) on the test data at each horizon step. Use the helper function `computeRRSE`

(shown at the end of this example). The RRSE indicates how well a model performs relative to the simple model, which always predicts the average of the true values. In particular, when the RRSE is less than 1, the model performs better than the simple model.

holdoutRRSE = cvloss(holdoutMdl,LossFun=@computeRRSE)

`holdoutRRSE = `*1×3*
0.4797 0.5889 0.6103

At each horizon, the direct forecasting model seems to perform better than the simple model.

For each test set observation, predict the temperature value using the corresponding model in `holdoutMdl.Learners`

.

predictedY = cvpredict(holdoutMdl); predictedY(450:end,:)

`ans=`*116×3 table*
TemperatureF_Step1 TemperatureF_Step2 TemperatureF_Step3
__________________ __________________ __________________
NaN NaN NaN
NaN NaN NaN
NaN NaN NaN
41.063 39.758 41.234
33.721 36.507 37.719
36.987 35.133 37.719
38.644 34.598 36.444
38.917 34.576 36.275
45.888 37.005 38.34
48.516 42.762 41.05
44.882 46.816 43.881
35.057 45.301 47.048
31.1 41.473 42.948
31.817 37.314 42.946
33.166 38.419 41.3
40.279 38.432 40.533
⋮

Recall that only the latest 113 observations appear in the test set. For observations that do not appear in the test set, the predicted response value is `NaN`

.

For each test set, plot the true response values and the predicted response values.

tiledlayout(3,1) idx = test(holdoutPartition); nexttile plot(t(idx),Tbl.TemperatureF(idx)) hold on plot(t(idx),predictedY.TemperatureF_Step1(idx)) legend("True Response","Predicted Response", ... Location="eastoutside") xlabel("Date") ylabel("Temperature") title("Horizon 1") hold off nexttile plot(t(idx),Tbl.TemperatureF(idx)) hold on plot(t(idx),predictedY.TemperatureF_Step2(idx)) legend("True Response","Predicted Response", ... Location="eastoutside") xlabel("Date") ylabel("Temperature") title("Horizon 2") hold off nexttile plot(t(idx),Tbl.TemperatureF(idx)) hold on plot(t(idx),predictedY.TemperatureF_Step3(idx)) legend("True Response","Predicted Response", ... Location="eastoutside") xlabel("Date") ylabel("Temperature") title("Horizon 3") hold off

Overall, `holdoutMdl`

is able to predict the trend in temperatures, although it seems to perform best when forecasting one step ahead. If you are satisfied with the performance of the partitioned model, you can use the full `DirectForecaster`

model `Mdl`

for forecasting at time steps beyond the available data.

**Helper Function**

The helper function `computeRRSE`

computes the RRSE given the true response variable `trueY`

and the predicted values `predY`

. This code creates the `computeRRSE`

helper function.

function rrse = computeRRSE(trueY,predY) error = trueY(:) - predY(:); meanY = mean(trueY(:),"omitnan"); rrse = sqrt(sum(error.^2,"omitnan")/sum((trueY(:) - meanY).^2,"omitnan")); end

## Input Arguments

`CVMdl`

— Cross-validated direct forecasting model

`PartitionedDirectForecaster`

model object

Cross-validated direct forecasting model, specified as a `PartitionedDirectForecaster`

model object.

### Name-Value Arguments

Specify optional pairs of arguments as
`Name1=Value1,...,NameN=ValueN`

, where `Name`

is
the argument name and `Value`

is the corresponding value.
Name-value arguments must appear after other arguments, but the order of the
pairs does not matter.

**Example: **`cvloss(CVMdl,Mode="individual")`

specifies to return the loss
for each window and horizon step combination.

`LossFun`

— Loss function

`"mse"`

(default) | function handle

Loss function, specified as `"mse"`

or a function handle.

If you specify the built-in function

`"mse"`

, then the loss function is the mean squared error.If you specify your own function using function handle notation, then the function must have the signature

`lossvalue =`

, where:(Y,predictedY)`lossfun`

The output argument

`lossvalue`

is a scalar.You specify the function name (

).`lossfun`

`Y`

is an*n*-by-1 vector of observed numeric responses at a specific horizon step, where*n*is the number of observations (`CVMdl.NumObservations`

).`predictedY`

is an*n*-by-1 vector of predicted numeric responses at a specific horizon step.

Specify your function using

`LossFun=@`

.`lossfun`

**Data Types: **`single`

| `double`

| `function_handle`

`Mode`

— Loss aggregation level

`"average"`

(default) | `"individual"`

Loss aggregation level, specified as `"average"`

or
`"individual"`

.

Value | Description |
---|---|

`"average"` |
At each horizon step, if an observation is in more than one test set, the function averages the predictions for the observation over all test sets before computing the loss. |

`"individual"` |
Before computing loss values at each horizon step, the function does not average the predictions for observations that are in more than one test set. |

**Example: **`Model="individual"`

**Data Types: **`char`

| `string`

## Output Arguments

`L`

— Losses

numeric vector | numeric matrix

Losses, returned as a numeric vector or numeric matrix.

If

`Mode`

is`"average"`

, then`L`

is a vector of loss values containing the loss at each horizon step, averaged over all partition windows. At each horizon step, if an observation is in more than one test set, the function averages the predictions for the observation over all test sets before computing the loss.If

`Mode`

is`"individual"`

, then`L`

is a*w*-by-*h*matrix of loss values, where*w*is the number of partition windows and*h*is the number of horizon steps (that is, the number of elements in`CVMdl.Horizon`

). Before computing the loss values at each horizon step, the function does not average the predictions for observations that are in more than one test set.

## Version History

**Introduced in R2023b**

## See Also

`PartitionedDirectForecaster`

| `cvpredict`

| `DirectForecaster`

| `tspartition`

## MATLAB 명령

다음 MATLAB 명령에 해당하는 링크를 클릭했습니다.

명령을 실행하려면 MATLAB 명령 창에 입력하십시오. 웹 브라우저는 MATLAB 명령을 지원하지 않습니다.

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