Why does my FORTRAN code produce a different answer outside of MATLAB than inside of my MEX-file?

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When I run my FORTRAN code as a standalone executable, I receive a different answer than when the same code is called from inside my MEX-file.

Accepted Answer

MathWorks Support Team
MathWorks Support Team on 27 Jun 2009
This is due to how MATLAB sets up the floating-point operations in the CPU at startup, and is not a bug in MATLAB.
If you use the following C code in your FORTRAN program, you should see the same answers:
void ResetFPU()
{
const static int CtrlWord=0x123f;
__asm fninit //initialize fpu
__asm fnclex // clear fpu exceptions
__asm fldcw CtrlWord // Load_FPU_Control_Word;
}

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