Math.cos inaccurancy

Question

alert(Math.cos(Math.PI/2));

Why the result is not exact zero? Is this inaccurancy, or some implementation error?

Answer 1

Comparing calculated floating point numbers for equality is almost always a bad idea, since (as others have stated) they are approximations, and errors appear.

Instead of checking for a==b, check for equality to within a threshold that makes sense for your application, as with Math.abs(a-b) < .00001. This is good practice in any programming language that represents numbers as floating point values.

If you're storing integers in floating point variables and just adding, subtracting, and multiplying, they'll stay integers (at least until they go out of bounds). But dividing, using trig functions, etc., will introduce errors that must be allowed for.

-m@