MATLAB: Mex mxGetField do loop

mex fortran do lopp mxgetfield struct

Hello,

I'm trying to use a do loop in my mex function that will take the values passed via a struct form from matlab. The matlab struct is as follows:

TurbineComponents.Blade(1).Position = ...
TurbineComponents.Blade(1).Orientation = ...
etc

I try the following as my do loop in the mex file:

              Do J = 1, NumBl
              Blade1_pr = mxGetField(prhs(ArgNum),1,'Blade(J)')
              b1p_pr = mxGetField(Blade1_pr,1,'Position')
              b1p_ptr = mxGetPr(b1p_pr)
              b1o_pr = mxGetField(Blade1_pr,1,'Orientation')
              b1o_ptr = mxGetPr(b1o_pr)
              b1v_pr = mxGetField(Blade1_pr,1,'RotationVel')
              b1v_ptr = mxGetPr(b1v_pr)
              b1t_pr = mxGetField(Blade1_pr,1,'TranslationVel')
              b1t_ptr = mxGetPr(b1t_pr)
             call mxcopyptrtoreal8(b1p_ptr,TurbineComponents%Blade(J)%Position,size2)
             call mxcopyptrtoreal8(b1o_ptr,TurbineComponents%Blade(J)%Orientation,size3)   
             call mxcopyptrtoreal8(b1v_ptr,TurbineComponents%Blade(J)%RotationVel,size2)
             call mxcopyptrtoreal8(b1t_ptr,TurbineComponents%Blade(J)%TranslationVel,size2)
             end Do

The problem is coming from the first line of code, "Blade(J)" I believe. Is there a way to work around the field name?

Best Answer

Get Blade using the J as the index. E.g.,

Blade1_pr = mxGetField(prhs(ArgNum),J,'Blade')

Related Solutions

MATLAB: How to input and output variable in mex function

Some issues:

    b       = mxGetPr(plhs[1]);
    d       = mxGetPr(plhs[2]);

The above lines crash MATLAB when you try to use b and d downstream because plhs[1] and plhs[2] haven't been created. The plhs variables are output variables that you the programmer need to create before you access them. So, create them first. E.g.,

    if( nlhs < 3 ) {
        mexErrMsgTxt("Need to specify three output variables");
    }
    plhs[0] = mxCreateDoubleMatrix(ynum,1,mxREAL);
    plhs[1] = mxDuplicateArray(prhs[1]);
    plhs[2] = mxDuplicateArray(prhs[3]);
    x       = mxGetPr(plhs[0]);
    b       = mxGetPr(plhs[1]);
    d       = mxGetPr(plhs[2]);

Then of course you don't need these earlier lines at all:

    b       = mxGetPr(prhs[1]);
        :
    d       = mxGetPr(prhs[3]);

And, to make your mex routine more robust, you should be checking the number and class and size of all of your inputs before using them downstream in your code.

MATLAB: MEX – Multidimensional Array passing to Fortran

A couple of options:

--------------------------------------

1)

See this FEX submission:

http://www.mathworks.com/matlabcentral/fileexchange/25934-fortran-95-interface-to-matlab-api-with-extras

To use a MATLAB 3D variable passed in to the mex function, e.g.:

use MatlabAPImx
real*8, pointer :: X(:,:,:)
X => fpGetPr3(prhs(1)) ! Does not copy the data

Then you can use X as a regular read-only Fortran variable since it is pointing directly at the data area of the original MATLAB variable in the workspace. I.e., no copy is made. If you need to alter the contents of X then use the copy version of the function instead with an appropriate deallocation at the end:

use MatlabAPImx
real*8, pointer :: X(:,:,:)
X => fpGetPr3copy(prhs(1)) ! Copies the data
   ! use/modify X
call fpDeallocate(X)

To copy a 3D Fortran array back to an output variable:

use MatlabAPImx
   ! X is a 3D Fortran real*8 variable
plhs(1) = mxArray(X)

To copy the input to a new matrix, modify it as a Fortran 3D variable, and return the result back to MATLAB you could do this:

use MatlabAPImx
real*8, pointer :: X(:,:,:)
plhs(1) = mxDuplicateArray(prhs(1)) ! Copies the data
X => fpGetPr3(plhs(1)) ! Points to the new copy
   ! use/modify X

--------------------------------------

2)

Manually get and copy the contents back & forth using mxGetNumberOfDimensions, mxGetDimensions, mxGetPr, mxCopyReal8ToPtr, mxCopyPtrToReal8, and Fortran allocated variables as necessary. Or some combination of the above with the %VAL() construct if you want to avoid data copies. It gets ugly so I will not attempt to write all of the details here.

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