Thanks! and yes z_i and q_i would depend on i, but for the purposes of the derivation they can just be symbols.
On Tuesday, June 4, 2013 11:23:49 PM UTC-4, Aaron Meurer wrote: > > I'd consider this to be a bug. I'm sure a call to doit() was added in > there to make Integral(x, x).diff(x) return just x, but it's clearly > annoying. > > I'm assuming you mean for q_i and z_i to mean that these things depend > on i. One way would be to actually use a function. Unfortunately, > there seem to be another bug: > > In [5]: z_i = Function('z')(i) > > In [6]: q_i = Function('q')(i) > > In [7]: a_k = Sum(-q_i*z_i/k,(i,1,m)) > > In [8]: print a_k.diff(z_i) > 0 > > I opened https://code.google.com/p/sympy/issues/detail?id=3867 and > https://code.google.com/p/sympy/issues/detail?id=3868 for these. > > Aaron Meurer > > On Tue, Jun 4, 2013 at 10:11 PM, Jeremy <laf...@gmail.com <javascript:>> > wrote: > > Hello, > > > > I am a new sympy user and am trying to work out a derivation using > IPython3 > > in a notebook. > > > > > > I have an expression: > > a_k = Sum(-q_i*z_i/k,(i,1,m)). > > > > I want a_k.diff(z_i), however the Sum gets evaluated and I get > m*(otherwise > > correct stuff), and of course the sum goes away. > > > > I thought that using Sum() instead of summation(), the expression would > not > > evaluate. I guess .diff() causes the expression to evaluate? Is there a > way > > around this problem? > > > > If it was this one expression I would just make temp = stuff_inside_sum > and > > .diff() that, but it is nested in yet another Sum(). Eg. phi = > > Sum(a_k/x,(k,1,oo)). > > > > Any help would be appreciated, > > 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 sympy+un...@googlegroups.com <javascript:>. > > To post to this group, send email to sy...@googlegroups.com<javascript:>. > > > Visit this group at http://groups.google.com/group/sympy?hl=en-US. > > For more options, visit https://groups.google.com/groups/opt_out. > > > > > -- 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 sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. Visit this group at http://groups.google.com/group/sympy?hl=en-US. For more options, visit https://groups.google.com/groups/opt_out.