[Numpy-discussion] Arcos returns nan
João Quinta da Fonseca
Fri Mar 28 04:20:23 CDT 2008
I have a function that returns the dot product of two unit vectors.
When I try to use arcos on the values returned I sometimes get the
"Warning: invalid value encountered in arccos", and the angle
returned is nan. I found out that this happens for essentially co-
linear vectors, for which the dot product function returns 1.0. This
looks like 1.0 no matter how I print it but if I do: >>N.dot(a,b)>1,
I get: >>True.
Now I guess this arises because of the way computers store floats but
shouldn't numpy take care of this somehow? Is it a bug? I don't seem
to have this problem with Matlab or Fortran.
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