I am writing a program to find the product of matrices in FORTRAN77.

It compiles, but I can't run it.

The error that came out is as follows.

The NOSTRICT option (default at OPT (3)) has the potential to alter the semantics of a program. Please refer to documentation on the STRICT/NOSTRICT option for more information.

what's the meaning of this?
Why can't I compile it but not?

  • Answer # 1

    If the optimization level is 3, it is a warning that the calculation is not always performed according to the formula in the program, and mathematically equivalent transformation may be performed, so first lower the optimization level and opt (0) or debug. It is recommended to try it in a mode.

    If that doesn't work, it's a problem other than this warning.

    Even if the formulas are mathematically equivalent on real numbers (complex numbers), the formulas may not be equivalent in the case of floating-point arithmetic, so the calculation results may not always match. The compiler warns me just in case.