Why does the MOD function from the Math Function

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krishna_patel - 2021-09-17T11:54:50+00:00
Question: Why does the MOD function from the Math Function

Why does the MOD function from the Math Function block return unexpected results with negative inputs in Simulink? I have a model with a MOD block. The inputs to the block are two constant values, for example -10 and 100. The output of the block is 90. I would have expected the result to be 10. Why is 90 returned?  

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    • Expert Answer

    Profile picture of Kshitij Singh Kshitij Singh answered . 2025-11-20

    The results returned from the Simulink MOD function are consistent with the MATLAB MOD function and the description from the help:
     
    MOD(x,y) is x - n.*y 
where n = floor(x./y) if y ~= 0.
    As a workaround, you can use the REM function in the Math Function block. As long as the operands X and Y are of the same sign, the function mod(X,Y) returns the same result as does rem(X,Y). However, for positive X and Y, mod(-X,Y) = rem(-X,Y)+Y.
     


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