Calling a Matlab function in Fortran using mex tool

Hi!

Using the MATLAB Engine API for Fortran, I am trying to call a simple Matlab function from a Fortran code.

I followed the fengdemo example found here : https://fr.mathworks.com/help/matlab/matlab_external/build-and-run-fortran-engine-applications-on-linux.html . It worked, so I want to adapt my Fortran code to call a specific Matlab script I wrote.

My Matlab script call_fortran.m is very simple: it takes x as an entry and multiplies it by 2:

function multiply = call_fortran(x)
multiply = 2*x;
end

I want my Fortran code to generate a variable my_x, open a Matlab session, send the variable to the workspace, apply the function call_fortran and display the result. Using the fengdemo.f code, I wrote

program main

C     Declarations
implicit none

mwPointer engOpen, engGetVariable, mxCreateDoubleMatrix
mwPointer mxGetPr
mwPointer ep, my_x  ! ep: variable linked to engOpen, starting a Matlab session, my_x: variable que je veux donner a Matlab

double precision my_x
integer engPutVariable, engEvalString, engClose
integer temp, status
mwSize i
my_x = 6

ep = engOpen('matlab ')

if (ep .eq. 0) then
    write(6,*) 'Can''t start MATLAB engine'
    stop
    endif
    
    C     Place the variable my_x into the MATLAB workspace
    status = engPutVariable(ep, 'my_x', my_x)
    C
    if (status .ne. 0) then 
        write(6,*) 'engPutVariable failed'
        stop
    endif
    ! My issue now is to call the correct Matlab script
    C nlhs = 1
    C plhs = 1
    C nrhs = 1
    C prhs = 1
    C integer*4 mexCallMATLAB(nlhs, plhs, nrhs, prhs, functionName)

So I have my my_x, I send it to Matlab, but how do I apply the call_fortran.m function and get the new value of my_x ?

Thank you in advance for your help!

[James Tursa]

This appears to be the same post as

https://www.mathworks.com/matlabcentral/answers/1641205-calling-a-matlab-function-in-fortran?s_tid=srchtitle

[Nafalai]

Yes, thanks very much for your detailed answer!