Create Alternative Models to Compare

Build a Selection of Models

After you have fitted and examined a single model (either one- or two-stage or point-by-point), you will normally want to create more models to search for the best fit.

To create alternative models, in the Model Browser model views, use the Common Tasks links.

Use the Create Alternatives ( ) option to build a selection of alternative models to compare. Find Create Alternatives in the Common Tasks pane, the toolbar, or the Model menu.

  1. From any global model node (before calculating MLE), click Create Alternatives in the Common Tasks pane.

  2. In the Model Template dialog box, select a template to build a selection of models. There are predefined templates for polynomials, radial basis functions, hybrid radial basis functions, and Gaussian process models. You can also create your own templates of any models you choose, or use model types in the current project.

    To build a selection of model types, click New, then click OK.

  3. Observe the default list of several models. Add models if desired, then click OK.

  4. In the Model Selection dialog box, select the criterion for choosing the best child node e.g., PRESS RMSE, and click OK.

    The toolbox builds the models and selects the best using your selection criteria.

    Note

    The toolbox builds models in parallel if you have Parallel Computing Toolbox™.

  5. Assess all the fits in the Alternative Models list in case you want to choose an alternative as a better fit.

Note

After you start building models from any template, you can always click Stop to abort model building if the process is taking too long.

You can also create individual new models. Create child nodes by clicking the Add Model common task in modeling nodes. The Model Setup dialog box appears where you can change the type and settings. Repeat this for multiple child nodes to create a selection of different model types fitted to the same data.

Common Tasks links for creating alternative models vary depending on the model type:

  • To add a selection of alternatives for one-stage models, click Create Alternatives.

  • For two-stage models:

    • To add a selection of alternatives for each response feature node, at the local node, click Build Global Models.

    • To add local models, at the response node, click New Local Model.

  • To add point-by-point models, click Edit Model and then add to the list of models.

Create a Model Template

Create a template to build several model types, and save the template for reuse.

  1. From any global model node (before calculating MLE), click Create Alternatives in the Common Tasks pane.

  2. In the Model Template dialog box, click New then click OK.

    The Multiple Model Setup dialog box shows the default list of point-by-point model types so that you can try several models:

    • Poly2 with Stepwise: Min PRESS

    • Poly3 with Stepwise: Min PRESS

    • Hybrid RBF with nObs/3 centers

    • Gaussian process models (using defaults)

  3. To add models to the list, click Add to open the Model Setup dialog box, where you can select any model type available for the number of inputs. Click OK to add the model and return to the Multiple Model Setup dialog box.

  4. Click Add again to repeat the process to add as many different models as you like. Click Edit Model to change the settings for any models in the list.

  5. When you are satisfied with the list of model types, click OK in the Multi-Model Settings dialog box. The toolbox builds your chosen selection of model types as a selection of child nodes of the currently selected model node.

  6. The Model Selection dialog box appears, where you can select the criterion for choosing the best child node. Use the drop-down menu to select from the available criteria (such as from PRESS RMSE, RMSE, Box-Cox, Observations, or Parameters). You can select additional criteria to appear here using the Summary Statistics options, from the Model menu. See Summary Statistics. Click OK to accept the chosen criterion.

You can also save templates of models you have already built.

  1. From any global or one-stage model with child nodes, select Model > Create Template. You can save the child node model types of your currently selected modeling node as a template.

  2. To find your user-defined templates and build all those model types again for any global model you choose, use the Model Template dialog box. You can set the default directory where the toolbox looks for templates (and models, data, and projects) using File > Preferences

    You can use the Browse button to find stored templates that are not in the default folder. Select your template and click OK. The models are built and the Model Selection dialog box appears, where you can select the criterion for choosing the best child node.

Polynomial Template

Use the polynomial template in the Model Template dialog box to build several polynomials of different orders.

  1. Select Polynomials and click OK. The Model Building Options dialog box opens where you can specify the model settings.

  2. Choose the minimum and maximum order of the polynomials you want to build, and whether to use Stepwise settings. For example, if you choose 1 and 5 as the minimum and maximum polynomial order, 5 child node models are built (linear, quadratic, cubic, and so on). If you choose a Stepwise setting (e.g. Minimize PRESS), it is applied to all child models.

  3. Click Build and the models are built. The Model Selection dialog box appears; select the criterion for choosing the best child node.

RBF Template

In the Model Template dialog box, you can use the RBF template to build several radial basis function models with varying maximum numbers of centers and/or different kernels.

  1. Select RBF and click OK. The Model Building Options dialog box opens where you can specify the model settings.

  2. Enter a vector in the edit box to specify the maximum numbers of centers for each child model. This can be a MATLAB® expression including the number of observations, e.g. 10:10:nObs/2.

  3. If the current model node is an RBF, the same model settings are used by default. Click Model Settings to open the Radial Basis Function Model Settings dialog box, where you can view and change all the model parameters such as kernel and widths. See Types of Radial Basis Functions.

  4. Select the check box Build all kernels to create child models with the specified range of centers for each kernel type.

  5. Click Build and the models are built. The Model Selection dialog box appears, where you can select the criterion for choosing the best child node.

Hybrid RBF Template

In the Model Template dialog box, you can use the Hybrid RBF template to build several hybrid radial basis function models with varying maximum numbers of centers and/or different kernels.

  1. Select Hybrid RBF and click OK. The Model Building Options dialog box opens where you can specify the model settings.

  2. Enter a vector in the edit box to specify the maximum numbers of centers for each child model. This can be a MATLAB expression including the number of observations, e.g. 10:10:nObs/2.

  3. If the current model node is a hybrid RBF, the same model settings are used by default. Click Model Settings to open the Hybrid RBF Model Settings dialog box, where you can view and change all the model parameters such as kernel and widths (and the order of the polynomial part of the model on the Linear Part tab). See Hybrid Radial Basis Functions.

  4. Select the check box Build all kernels to create child models with the specified range of centers for each kernel type.

  5. Click Build and the models are built. The Model Selection dialog box appears, where you can select the criterion for choosing the best child node.

Free Knot Spline Template

In the Model Template dialog box, you can use the Free Knot Spline template to build several free knot spline models of different numbers of knots. Only available for models with a single input factor.

  1. Select Free Knot Spline and click OK. The Model Building Options dialog box opens where you can specify the model settings. If the current model node is a free knot spline, the same model settings are used by default.

  2. Choose the initial and final number of knots. For example, if you specify the initial and final numbers of knots as 1 and 5, five child nodes are built, one with one knot, one with two.

  3. Click Build and the models are built. The Model Selection dialog box appears, where you can select the criterion for choosing the best child node.

Gaussian Process Template

In the Model Template dialog box, select the Gaussian Process template to build a selection of Gaussian process models. You can choose to build all kernel functions and basis functions, or select a kernel or basis function.

Model Browser Template

In the Model Template dialog box, you can use the Model Browser template to build a copy of an existing set of child model types in the current project.

  1. Select Model Browser and click OK.

  2. The Model Tree dialog box opens. Select a model from the model tree that has the child node model types you want to build. You can also use this template to select a local multiple model node to copy. Click OK to return to the Model Template dialog box.

  3. Click Build and the models are built. The Model Selection dialog box appears, where you can select the criterion for choosing the best child node.