math.sin and math.cos error

[yegorf1]

Hi, all I'm running love 0.8.0 and when I launched this:

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print('math.sin 0: ' .. math.sin(0))
print('math.sin 90: ' .. math.sin(math.pi / 2))
print('math.sin 180: ' .. math.sin(math.pi))
print('math.sin 270: ' .. math.sin(math.pi / 2 * 3))
print('math.cos 0: ' .. math.cos(0))
print('math.cos 90: ' .. math.cos(math.pi / 2))
print('math.cos 180: ' .. math.cos(math.pi))
print('math.cos 270: ' .. math.cos(math.pi / 2 * 3))

I see this:

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math.sin 0: 0
math.sin 90: 1
math.sin 180: 1.2246467991474e-16
math.sin 270: -1
math.cos 0: 1
math.cos 90: 6.1232339957368e-17
math.cos 180: -1
math.cos 270: -1.836970198721e-16

What's the error?
Thanks (:

[markgo]

http://en.wikipedia.org/wiki/Floating_p ... y_problems

[bekey]

-snip-

[Robin]

No, Lua trig functions work with radians.

[XCaptain]

shouldn't there be some conversion from radians to degrees too?

math.rad(degrees)
This will return x degrees in radians.
math.deg(radians)
This is just the opposite.

[bekey]

-snip-

[Plu]

Short answer: rounding errors.

This: 1.2246467991474e-16
Is this: 0.00000000000000012246467991474

Which is 0 for all practical purposes.

I'm guessing (but I'm not sure) that even Lua will agree and say it equals zero if you compare with it. Otherwise, you'd have to use a bit of floating point comparisons (ie; sin(x) <= 0.0000001) or make an exact comparison against the input for the function before you calculate the sin value of it.

[Robin]

I'm guessing (but I'm not sure) that even Lua will agree and say it equals zero if you compare with it.

Nope:

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> print(1.2246467991474e-16 == 0)
false

Floating point comparisons are finicky, and you usually want to compare them within an epsilon (basically, a very small value that is the margin of error you choose).