[Numpy-discussion] Piecewise functions.
Paulo J. S. Silva
pjssilva at ime.usp.br
Fri Sep 23 06:34:19 CDT 2005
Here is a slightly different solution, that is easier to my eyes and
that can handle arguments in arbitrary order.
It requires numarray (as it uses array indexing). If I understand well
it should work woth the new scipy-core (Numeric3), but I haven't it
compiled here.
Obs: Probably f2 implementation is faster than f1.
Best,
Paulo
----
from numarray import *
def f1(x):
"""Implementation of:
-1/(x-pi) for x < pi
1/(x-pi) for x > pi
"""
result = zeros(len(x), x.typecode())
# First solution, probably slower, but clear.
result[x < pi] = -1/(x[x < pi]-pi)
result[x > pi] = 1/(x[x > pi]-pi)
return result
def f2(x):
"""Second Iplementation of:
-1/(x-pi) for x < pi
1/(x-pi) for x > pi
"""
result = zeros(len(x), x.typecode())
# Second solution, probably faster as where returns only
# the correct indexes.
small = where(x < pi)
big = where(x > pi)
result[small] = -1/(x[small]-pi)
result[big] = 1/(x[big]-pi)
return result
x = arange(0, 10, 1, Float)
print f1(x)
print f2(x)
print abs(1/(x-pi))
# It uses the default value for pi.
api = array([pi])
print f1(api)
print f2(api)
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