In Fortran you should never pass literal constant arguments to the API functions since they can vary in size among different platforms. You can get away with this in C/C++ because arguments are passed by value and are automatically converted to the correct type, but you can't get away with this practice in Fortran. Instead of doing this:
mVx0 = mxCreateDoubleMatrix(1, 1, 0)
call mxCopyReal8ToPtr(Vx0, mxGetPr(mVx0), 1)
you should be doing this:
mwPointer, external :: mxCreateDoubleMatrix, mxGetPr
mwSize :: one = 1
integer*4 :: complexity = 0
:
mVx0 = mxCreateDoubleMatrix( one, one, complexity )
call mxCopyReal8ToPtr( Vx0, mxGetPr(mVx0), one )
That way the integer arguments should always be the correct type regardless of platform.
You might also be interested in this Fortran 95 interface package:
