[Numpy-discussion] sort bug
Thu Apr 26 03:26:59 CDT 2007
Anton Sherwood wrote:
> This code --
> adj = [ [eval(y) for y in x.split()] for x in infile ]
> val,vec = numpy.linalg.eig(adj)
> master = zip( val, vec.transpose() )
> *sometimes* gives this error:
> Traceback (most recent call last):
> File "3work.py", line 14, in <module>
> ValueError: The truth value of an array with more
> than one element is ambiguous. Use a.any() or a.all()
> What does sort() care about truth values?!
The sort method on lists basically uses cmp(x,y) to determine sort
order. In this case, I suspect you are getting errors whenever you have
equal-valued eigenvalues so the comparison has to go to the second item
in the tuple (which is the array).
cmp(x,y) must return -1, 0, or 1 which doesn't work on arrays with more
than 1 element because it is ambiguous. Thus you get this error.
The operation is undefined. What do you actually want to do when you
have equal-valued eigenvalues?
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