Why does the MOD function from the Math Function block return unexpected results with negative inputs in Simulink?

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?

Answer 1

[MathWorks Support Team]

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.