Rounding behaves differently with or without the number of decimals.

[jpkolbush]

Hello,

I found that rounding behaves differently depending on if you pass in 0 or not.

If you evaluate mathjs.round(-2.5) it returns -2
However if you evaluate mathjs.round(-2.5, 0) it returns -3

We wish to use the later case (always rounding away from 0) so its not a pressing issue, as we can just pass in the extra parameter. But I figured it should be brought to your attention.

[josdejong]

That's odd, I would indeed want consistent behavior there. I would expect mathjs.round(-2.5) to return -3 indeed. Thanks for reporting.

Anyone interested in digging into this issue?

[Yaffle]

Math.round(-2.5) === -2 :

If two integer Number values are equally close to x, then the result is the Number value that is closer to +∞

while the mathjs.round(-2.5, 0) uses https://github.com/josdejong/mathjs/blob/develop/src/function/arithmetic/round.js#L53 , probably

[josdejong]

Turns out round(x) did simply use the built-in Math.round instead of the method used for round(x, n), which allowed for inconsistent behavior.

See fix: 7d00987

Both numbers and BigNumbers now have the following behavior (similar to Matlab and Python, and unlike Mathematica which rounds -2.5 to 2):

math.round(2.5) // number 3
math.round(-2.5) // number -3
math.round(math.bignumber(2.5)) // BigNumber 3
math.round(math.bignumber(-2.5)) // BigNumber -3

[josdejong]

Should be fixed now in v5.5.0.