On 21/02/07, WolfgangZillig <[EMAIL PROTECTED]> wrote: > Hi, > > I'm quite new to numpy/scipy so please excuse if my problem is too obvious. > > example code: > > import numpy as n > print n.sin(n.pi) > print n.cos(n.pi/2.0) > > results in: > 1.22460635382e-016 > 6.12303176911e-017 > > I've expected something around 0. Can anybody explain what I am doing > wrong here?
Well, nothing. It is around zero. Try (without numpy) >>> (1.+1e-16)-1. 0.0 That is, for floating-point numbers, 1e-16 is about the fractional error you can expect from any calculation, and since pi is of order unity, you should expect its representation to have about that big an error on it; feed that through sin and you get an error of about the same size. Or, to see more clearly, try taking (on a pocket calculator, say) sin(3.14) (or even sin(pi)). Roundoff error is a basic fact of life in numerical computations. Anne _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
