Multiple dispatch problem when trying to call the feval function with a LinearModel as an argument.

I set up a workflow where I am using feval to call functions programmatically and ran into a major stumbling block with one particular function call. I've isolated the problem below and explain what I think is happening.

x = 200;
[y_mean, y_sigma, y_int] = lin_model_predict(model, x, vars, params);  % works fine

assert(round(y_mean, 4) == 139.7200);
assert(isequaln(y_sigma, nan));
assert(isequal(round(y_int, 4), [137.5938  141.8462]));

% Test again using feval
f_name = "lin_model_predict";  % this will later be set programatically
[y_mean, y_sigma, y_int] = feval(f_name, model, x, vars, params);  % raises error

The error raised is:

Error using classreg.regr/CompactPredictor/feval

Too many output arguments.

Error in test_lin_models (line 46)

[y_mean, y_sigma, y_int] = feval(f_name, model, x, vars, params);

So instead of calling the normal feval function, it seems to be calling the feval method of CompactPredictor class. From the documentation in /Applications/MATLAB_R2021b.app/toolbox/stats/classreg/+classreg/+regr/CompactPredictor.m:

function yPred = feval(model,varargin)
%FEVAL Evaluate model as a function
%    YPRED = FEVAL(M,X1,X2,...Xp) computes an array YPRED of predicted
%    values from the regression model M using predictor values X1, X2, ...,
%    Xp, where P is the number of predictors in M.  Each X argument must be
%    the same size, and must have the same type as the corresponding
%    predictor variable. The size of the YPRED output is the same as the
%    common size of the X inputs.

I guess this is some kind of multiple dispatch problem. How can I avoid this? My code works for other functions. I think it is only because my model variable is an instance of LinearModel. Is there a way to specifically call the main feval function, built-in (/Applications/MATLAB_R2021b.app/toolbox/matlab/lang/feval)?

Answer 1

[Bill Tubbs]

There are some good suggested solutions to this from Cris Luengo on this parallel stackoverflow post:

• MATLAB "Too many output arguments" error when calling a function using feval