| for optional arguments

[Alfonso Sánchez-Peñalver]

Hi, I'm starting to program a class, and I am having trouble when defining the setup() function for the class with an optional argument. The code in my .mata is

version 15
mata:
class nelogit
{
    // Definition of variables that are common to all estimators, thus
    // making them protected so they can inherit them.
    protected:
        real matrix X, S                                                        // explanatory variables and scale variables
        real colvector b, bS, g                                                    // coefficients, scaled coefficients, and gradient
        real matrix V, H                                                        // Variance and Hessian
        real colvector y                                                        // vector of the dependent variable
        real scalar j                                                            // number of alternatives
        real scalar ll0, ll                                                        // log-likelihoods of constants-only and estimated models
        real scalar r2                                                            // McFadden's pseudo-rsquared
    
    public void setup()
    
    // Functions implemented in this class
    private:
        real scalar ll0()                                                        // Returns the ll of constants-only model
        real scalar r2()                                                        // Returns McFadden's pseudo R-squared
}
// Setup functions for the class
void nelogit::setup(real colvector user_y,
    real matrix user_X,
    real scalar user_j |,
    real matrix user_S)
{
    this.y = user_y
    this.X = user_X
    this.j = user_j
    if (args()>3)
        this.S = user_S
    this.ll0 = this.ll0()
}
......

end

where the dots indicate other functions, none of which have | anywhere in them. When I "do" this file I get

. quiet do "`pdir'/nelogit.mata"
'|' found where ')' expected
(41 lines skipped)
r(3000);

end of do-file

r(3000);

As soon as I take the vertical line out it runs file of course, but the point is that I want the matrix user_S to be optional. If it's there we would be modeling scale heterogeneity if not we wouldn't.

[Joseph Coveney]

Put the pipe after the comma and on the next line.

    real scalar user_j,
    | real matrix user_S)

[Alfonso Sánchez-Peñalver]

Thanks Joseph Coveney !!!! I guess I should read the errata on Gould's book!!! Just saw that. It was driving me nuts.