Comment #14 on issue 2128 by jagermeistermeister: cannot integrate
piecewise function numerically
http://code.google.com/p/sympy/issues/detail?id=2128
Thanks asmeurer and mattpap, the in operator in combination with the
expression is what I'm looking for :)
Now I realise that I have been doing something the wrong way. The following
error message:
raise NotImplementedError, \
"Currently only supporting evaluation with only " \
"sym on one side of the relation."
is correct imho. Suppose I would like to integrate the following Piecewise
function on the interval [-oo, oo] wrt y:
⎧1 for x - y < 0
⎨
⎩0 for 1
I have no idea how to go about that mathematically (the x-y < 0 in the
condition makes it difficult for me). I think it's safe to say the
functionality for that is not implemented. But please correct me if I'm
mistaken.
Whenever I do f.subs(x, x-y) (where f is a Piecewise function), it
substitutes x in both the expression and the condition. This is expected
behaviour, but not the desired behaviour for me and I'm looking for a way
to only substitute x in the expression (not in the condition). Is this
possible somehow? If not, I could try to add that functionality.
Some background information about what I'm trying to do:
I have a Piecewise defined probability density function (pdf) of a random
variable. I want to add this random variable to another which also has a
Piecewise defined pdf (assuming they are independent). Mathematically, that
goes like this (suppose f(x) and g(x) are the pdfs of random variables X
and Y):
Z = X + Y
then the pdf h(x) of random variable Z is given by: h(x) = integrate(f(x-y)
* g(y), (y, -oo, oo) )
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