Predict Responses Using RegressionTree Predict Block

This example shows how to use the RegressionTree Predict block for response prediction in Simulink®. The block accepts an observation (predictor data) and returns the predicted response for the observation using the trained regression tree model.

Train Regression Model

Load the carbig data set, which contains measurements of cars made in the 1970s and early 1980s. Create a matrix containing the predictor variables and a vector of the response variable.

load carbig
X = [Acceleration,Cylinders,Displacement,Horsepower,Model_Year,Weight];
Y = MPG;

Train a regression tree model.

treeMdl = fitrtree(X,Y);

treeMdl is a RegressionTree model.

Create Simulink Model

This example provides the Simulink model slexCarDataRegressionTreePredictExample.slx, which includes the RegressionTree Predict block. You can open the Simulink model or create a new model as described in this section.

Open the Simulink model slexCarDataRegressionTreePredictExample.slx.

SimMdlName = 'slexCarDataRegressionTreePredictExample'; 
open_system(SimMdlName)

If you open the Simulink model, then the software runs the code in the PreLoadFcn callback function before loading the Simulink model. The PreLoadFcn callback function of slexCarDataRegressionTreePredictExample includes code to check if your workspace contains the treeMdl variable for the trained model. If the workspace does not contain the variable, PreLoadFcn loads the sample data, trains the tree model, and creates an input signal for the Simulink model. To view the callback function, in the Setup section on the Modeling tab, click Model Settings and select Model Properties. Then, on the Callbacks tab, select the PreLoadFcn callback function in the Model callbacks pane.

To create a new Simulink model, open the Blank Model template and add the RegressionTree Predict block. Add the Inport and Outport blocks and connect them to the RegressionTree Predict block.

Double-click the RegressionTree Predict block to open the Block Parameters dialog box. You can specify the name of a workspace variable that contains the trained tree model. The default variable name is treeMdl. Click the Refresh button. The dialog box displays the options used to train the tree model treeMdl under Trained Machine Learning Model.

The RegressionTree Predict block expects an observation containing 6 predictor values. Double-click the Inport block, and set the Port dimensions to 6 on the Signal Attributes tab.

Create an input signal in the form of a structure array for the Simulink model. The structure array must contain these fields:

• time — The points in time at which the observations enter the model. The orientation must correspond to the observations in the predictor data. So, in this example, time must be a column vector.

• signals — A 1-by-1 structure array describing the input data and containing the fields values and dimensions, where values is a matrix of predictor data, and dimensions is the number of predictor variables.

Create an appropriate structure array for the slexCarDataRegressionTreePredictExample model from the carsmall data set.

load carsmall
testX = [Acceleration,Cylinders,Displacement,Horsepower,Model_Year,Weight];
testX = rmmissing(testX);
carsmallInput.time = (0:size(testX,1)-1)';
carsmallInput.signals(1).values = testX;
carsmallInput.signals(1).dimensions = size(testX,2);

To import signal data from the workspace:

• Open the Configuration Parameters dialog box. On the Modeling tab, click Model Settings.

• In the Data Import/Export pane, select the Input check box and enter carsmallInput in the adjacent text box.

• In the Solver pane, under Simulation time, set Stop time to carsmallInput.time(end). Under Solver selection, set Type to Fixed-step, and set Solver to discrete (no continuous states).

For more details, see Load Signal Data for Simulation (Simulink).

Simulate the model.

sim(SimMdlName);

When the Inport block detects an observation, it directs the observation into the RegressionTree Predict block. You can use the Simulation Data Inspector (Simulink) to view the logged data of the Outport block.