Just compute the definite integral, and evaluate at the limits manually. That is, use integrate(1/(1-z), z).
However you're going to have problems because as Chris notes, log(1 - z) = log(-1) + log(z - 1) is not always valid (I think it may be true if z < 1, if I remember the rule correctly). The issue is that for real values, the integral of 1/x should be log(abs(x)) (this isn't true in the complex case, which is why SymPy doesn't return that value). I believe the result you get with the I*pi is mathematically correct. That is, if you plug in any real value for z, you'll get the same result as from -log(abs(z - 1)). Aaron Meurer On Fri, Feb 13, 2015 at 8:15 PM, Chris Smith <[email protected]> wrote: > You can do a little manual simplification like this: > > >>> integrate(1/(1-z),(z,0,z)) > -log(z - 1) + I*pi > >>> exp(_) > -1/(z - 1) > >>> 1/(-1/_/-1) # the badger-face inversion :-) > 1/(-z + 1) > >>> log(_) > log(1/(-z + 1)) > > But that can't simplify to -log(1-z) because that is not valid unless 1-z > is positive. > > >>> expand_log(log(1/Dummy(positive=True))) > -log(_Dummy_85) > >>> expand_log(log(1/Dummy(nonnegative=True))) > log(1/_Dummy_86) > >>> expand_log(log(1/Dummy(negative=True))) > log(1/_Dummy_107) > > > On Friday, February 13, 2015 at 6:37:56 PM UTC-6, Ian Bell wrote: >> >> There was an embedded image, but clearly that didn't work. >> >> >> integrate(1/(1-z),(z,0,z)) >> >> was the command. I used a picture to show that you get an imaginary term >> as part of the return value >> >> On Friday, February 13, 2015 at 4:11:54 PM UTC-7, Aaron Meurer wrote: >>> >>> >>> >>> On Fri, Feb 13, 2015 at 3:42 PM, Ian Bell <[email protected]> wrote: >>> >>>> I am trying to do an integration like this: >>>> >>> >>> Was there supposed to be something here? It's just showing up as empty >>> space for me. >>> >>> Aaron Meurer >>> >>> >>>> >>>> >>>> >>>> Ultimately the result I should be able to get is -log(1-z) >>>> >>>> Manual integration shows that you can integrate(1/(1-z),z) -> >>>> -log(z-1), evaluation at the limits yields -log(z-1) - (-log(-1)) which you >>>> can simplify to -log(1-z). How can I tell sympy to delay evaluation until >>>> after it has done the simplification? I guess that it first does log(-1), >>>> which it isn't happy about... >>>> >>>> Ian >>>> >>>> -- >>>> 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 http://groups.google.com/group/sympy. >>>> To view this discussion on the web visit https://groups.google.com/d/ >>>> msgid/sympy/fdbada4e-6ba0-4de5-835f-5121aaa022ce%40googlegroups.com >>>> <https://groups.google.com/d/msgid/sympy/fdbada4e-6ba0-4de5-835f-5121aaa022ce%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> -- > 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 http://groups.google.com/group/sympy. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/95372b64-3f66-484b-b8c2-1efff0d3a87f%40googlegroups.com > <https://groups.google.com/d/msgid/sympy/95372b64-3f66-484b-b8c2-1efff0d3a87f%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- 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 http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAKgW%3D6JROf%2BWCPES%3DUKXZWn18Rt3NbZzCj75mkCBmrafKj-FxA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
