# Trig inaccuracy

I am using the trig functions in Snap, and noticed that they are not completely accurate. For example, sin(180) should return 0, not a really small number. Do this have to do with the fact that JavaScript uses radians, but Snap uses degrees? For example returns 0 because 0 is the same in degrees and radians. However returns a decimal because (I think) 180 must be converted to π radians. Just thought I should point this out.

Yes, I keep telling Jens that the right way to do trig functions in degrees is to start by converting the angle in degrees to something in the range [0, 45], which may involve swapping sin with cos and may involve changing the sign of the eventual result, then multiply by π/180, which is how Prof. Kahan says to do it, but he (Jens) doesn't believe me that it matters.

It seems as if such a small error would not matter, but the problem is not that is an error of 10^-16 at an arbitrary number, but the fact that sin(0) is not 0, which is a known value. For example would never report true, even though it is within one quadrillionth of 0.

Eh?

Here is what I learned in my computer science course: when using floating-point arithmetic, check for close enough, not equality.

Instead of [scratchblocks]<(number) = (what I want)>[/scratchblocks],

do [scratchblocks]<([abs v] of ((number) - (what I want))) < [0.001]>[/scratchblocks].

Sorry, I meant to say that sin of 180 is not 0:

Yeah I knew that, just not quite awake. Sorry. But my answer about how to compute trig functions of angles in degrees still stands.

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