I convert degrees to radians (degrees * Math.PI/180) but why does the following:
Math.cos(90 * Math.PI/180)
yield 6.123031769111... and not zero?
I'm trying to perform 2D rotations uses matrixes and the results are completely out of whack.
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2You should show more code so we can see some context. – Gabe Mar 11 '12 at 05:24
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4@Gabe- Actually, the above code is sufficient. Try typing it into a JS console and you will indeed get the result shown above. – templatetypedef Mar 11 '12 at 05:27
3 Answers
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The output of
Math.cos(90 * Math.PI/180)
is
6.123031769111886e-17
Notice the e-17 at the end, which means that this number is 6.123 x 10-17. This is a number so vanishingly close to 0 that it's effectively 0. The reason that it's not identically 0 is due to rounding errors in the IEEE-754 double format which prevents you from getting an exact representation of π / 2 and causes minute rounding errors in the calculation of the cosine.
By the way - I was pretty surprised as well when the result came back starting with a 6! It's only after I looked at the very end that things started to make sense.
Hope this helps!
Daniel Fischer
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templatetypedef
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3+1. Maybe add something like `Math.cos(90 * Math.PI/180).toFixed(15)` as a simple solution? – Dagg Nabbit Mar 11 '12 at 06:02
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3
6.123233995736766e-17
is scientific notation for a very small number, close to zero. It is not exactly zero because of rounding errors and so forth.
Karl Knechtel
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