Today I was working on a little acoustics simulation patcher in Cycling 74’s Max, and part of the code required the use of a modulo function. No problem, right?
Problem. I originally wrote the code in Matlab, and I was porting it to Max; and the numbers just weren’t working properly. After getting rid of my own home-made bugs, it still wasn’t working…
Turns out that there seems to be a disagreement in the code community about how to do the modulo of a negative number.
The best indication of the problem I was facing is found on this page, where you can see that different languages come up with different answers for -13 mod 3 and 13 mod -3. The problem is that neither Max nor Matlab are in the list. So: here are the results of those two, to add to the list.
The results are:
| Language | 13 mod 3 | -13 mod 3 | 13 mod -3 | -13 mod -13 |
| Matlab | 1 | 2 | -2 | -1 |
| Max | 1 | -1 | 1 | -1 |
This means that Matlab behaves like Python, using the formula
mod(a, n) = a – n * floor(a / n)
whereas Max behaves like C and Java.
So, if you, like me, move back and forth between Matlab and Max, beware!