You can also just use the "manual" hint: >>> integrate(1/((1-z)),z,manual=True) -log(-z + 1)
On Friday, February 13, 2015 at 11:33:18 PM UTC-6, Aaron Meurer wrote: > > 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] > <javascript:>> 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] <javascript:>. >> To post to this group, send email to [email protected] <javascript:> >> . >> 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/9279f416-efa5-4cbe-b5bd-21894c1609c7%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
