In comment 1 you said you had to compute the range yourself. What do you mean and why did you have to do so?
Regarding a later comment about handing convolutions where different functions have different ranges, that *should* be handled with Piecewise. Perhaps you could give my `lts` branch in PR #12587 a try. A major overhaul of Piecewise is presented there. On Wednesday, June 7, 2017 at 10:35:16 AM UTC-5, [email protected] wrote: > I'm trying to write a generic function to convolve two functions (in one > dimension, for now) and came across a few issues I don't know how to solve. > Rather than give up, maybe I can start a discussion. Some Sympy follows: > > a , b = symbols('a b', positive=True) > f = exp(-a*x) > g = exp(-b*x) > integrate(f.subs(x,tau)*g.subs(x,t-tau), (tau,0,t)) > > > 1. I had to compute the range of integration myself (tau, 0, t). This > isn't a fatal problem, but piecewise doesn't have enough information to > compute it simply. (My long term solution is to propose a replacement for > the piecewise function, but I'm not there yet.) > > The answer is below: > > Piecewise((t*exp(-b*t), Eq(a, b)), (1/(a*exp(b*t) - b*exp(b*t)) - > 1/(a*exp(a*t) - b*exp(a*t)), True)) > > > The answer is correct, but there are problems trying to incorporate it > into a larger function. > > 2. It is not obvious in advance the answer will depend on whether a = b. > Is there some way to assume in advance that a=b or a!=b? > > 3. The second condition, True, isn't helpful. To understand what True > means, one has to keep track of the previous conditions. Is there some way > to replace the True with a != b. > > 4. This is a simpler question, but I can't figure it out. How do I > manipulate the second answer to my preferred form? > > (exp(-b*t)-exp(-a*t))/(a-b) > > Is there a simple way to do it programmatically? > > Thanks > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/7765826a-a078-4c41-8890-f79b9a2e19a3%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
