how to write mex function when input is a matlab function

I want to write a C code to replace the fzero function in matlab by using MEX function, while the function's form is an input in the C code, how can I specify it?

Currently my C code is like following:

#include "mex.h"
#include <stdio.h>
#include <stdio.h>
#include <math.h>

// secant method
double f_zero(double(*f)(double x),double a,double b, double error)
{
    double c;
    int count=0;
    if (f(a) * f(b)>0)
    {
        b = -b;
        } 
    c = (b*f(a)-a*f(b))/(f(a)-f(b));; 
    while(fabs(f(c))>error && count <100)
        {
            count = count+1;
            if (f(a)*f(c)<0)
            {
                b=c;
                }
            else
                {
                    a=c;
                    }
                c = (b*f(a)-a*f(b))/(f(a)-f(b));;
                }
                return c;
                
                }
                
                void mexFunction(int nlhs, mxArray* plhs[], int nrhs, const mxArray* prhs[])
                
                {
                    #define FCN_IN prhs[0]
                    #define x1 prhs[1]
                    #define x2 prhs[2]
                    #define x3 prhs[3]
                    #define Y_OUT plhs[0]
                    
                    Y_OUT = f_zero(FCN_IN,x1,x2,x3);
                    
                    }

suppose f = @(x) x*x + 3x-4;

how can I get f_zero_c(fun,-5,0,0.00001) in matlab?

Thanks a lot!

[Ive J]

Have you checked mex?

https://mathworks.com/help/matlab/call-mex-files-1.html

Answer 1

[James Tursa]

This can be done, but it will not be efficient. The basic problem is that C/C++ doesn't understand anything about MATLAB functions. You would have to write a wrapper function with callbacks to accomplish this, and the overhead of doing this would hardly make the effort worh it IMO. C/C++ function pointers cannot point to MATLAB functions directly ... they have to use the mexCallMATLAB( ) API function. So input/output arguments must be copied to/from mxArray types to accomplish the function evaulation. I.e., every time you want to call your f( ) function you have to invoke the mexCallMATLAB( ) function in the background. I would advise that you first learn how to write simple mex functions (e.g., multiply a number by 2, or add two numbers together) before you tackle something like writing your own fzero( ) replacement.