Re: [sage-support] Re: Simplifying log expressions
Dear Sage Developers: There seems to be a similar issue in Sage Version 4.8: sage: a=log(6)/(1+log(2)) sage: (6*exp(-a)-2^a).full_simplify() -(2^(log(3)/(log(2) + 1) + 1/(log(2) + 1))*3^(1/(log(2) + 1))*e^(log(2)^2/(log(2) + 1)) - 6)/(2^(1/(log(2) + 1))*3^(1/(log(2) + 1))) sage: (6*exp(-a)/2^a).simplify_full() 2^(log(2/3)/(log(2) + 1))*3^(log(2)/(log(2) + 1))*e^(-log(2)^2/(log(2) + 1)) Sincerely, Greg Marks | Greg Marks | | Department of Mathematics and Computer Science | | St. Louis University | | St. Louis, MO 63103-2007 | | U.S.A. | || | Phone: (314)977-7206 | | Fax: (314)977-1452 | | Web: http://math.slu.edu/~marks| -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
[sage-support] Re: Simplifying log expressions
In gmane.comp.mathematics.sage.support, you wrote: Dear Sage Developers: There seems to be a similar issue in Sage Version 4.8: sage: a=log(6)/(1+log(2)) sage: (6*exp(-a)-2^a).full_simplify() -(2^(log(3)/(log(2) + 1) + 1/(log(2) + 1))*3^(1/(log(2) + 1))*e^(log(2)^2/(log(2) + 1)) - 6)/(2^(1/(log(2) + 1))*3^(1/(log(2) + 1))) sage: (6*exp(-a)/2^a).simplify_full() 2^(log(2/3)/(log(2) + 1))*3^(log(2)/(log(2) + 1))*e^(-log(2)^2/(log(2) + 1)) Sage calls Maxima to do such kinds of computations. If one uses Maxima on these expressions directly, it does not come up any better than that. (Or perhaps one needs to know more about Maxima than I do). Best, Dmitrii Sincerely, Greg Marks -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] Re: Simplifying log expressions
On 01/15/12 13:18, JamesHDavenport wrote:
Thanks. Given that, here's the sagenb (4.7.2) version, showing the bug
(wrong when t is negative real):
sage: t=var('t')
sage: f=(1/2)*log(2*t)+(1/2)*log(1/t)
sage: f.full_simplify()
1/2*log(2)
I created a ticket for this here:
http://trac.sagemath.org/sage_trac/ticket/12322
Thanks for the example!
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[sage-support] Re: Simplifying log expressions
I was using sagenb,org, so the output isn't actually a SAGE session, but pasting from sagenb.org. It says it is 4.7.2. Glad it's fixed. I guess I ought to download a 4.8 if I'm really going to comment in more detail, given the apparent changes. On Jan 14, 1:47 am, Michael Orlitzky mich...@orlitzky.com wrote: On 01/13/2012 07:38 PM, JamesHDavenport wrote: Unfortunately, full_simplify has its own problems, notably with branch cuts. sage: f = (1/2)*log(2*t) + (1/2)*log(-t) sage: f.full_simplify() 1/2*log(2) In my session, I had the difference of two logarithms. In yours above, you've got the sum. Is that an actual sage session? I get something different on 4.8.alpha6: sage: f = (1/2)*log(2*t) + (1/2)*log(-t) sage: f.full_simplify() 1/2*I*pi + 1/2*log(2) + log(t) In the example below, with t=-1, both logs should have imaginary part pi and real parts log(2) and zero respectively? There's no global function for it, but what you want is to call full_simplify() on the expression. sage: f = (1/2)*log(2*t) - (1/2)*log(t) sage: f.full_simplify() 1/2*log(2) -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
[sage-support] Re: Simplifying log expressions
Unfortunately, full_simplify has its own problems, notably with branch cuts. sage: f = (1/2)*log(2*t) + (1/2)*log(-t) sage: f.full_simplify() 1/2*log(2) Unfortunately, when t=-1, we have the sum of the logarithms of two negative numbers, and therefore the imaginary part is 2i pi, not 0 On Jan 12, 10:24 pm, Michael Orlitzky mich...@orlitzky.com wrote: On 01/12/12 17:16, Tom Judson wrote: I would like to simplify the difference of two log expressions to show that I get a constant, but simplify((1/2)*log(2*t) - (1/2)*log(t)) just returns the expression. Does anyone know of an easy fix for this? Preferably, I would like something that Calculus II students could easily use. There's no global function for it, but what you want is to call full_simplify() on the expression. sage: f = (1/2)*log(2*t) - (1/2)*log(t) sage: f.full_simplify() 1/2*log(2) -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] Re: Simplifying log expressions
On 01/13/2012 07:38 PM, JamesHDavenport wrote: Unfortunately, full_simplify has its own problems, notably with branch cuts. sage: f = (1/2)*log(2*t) + (1/2)*log(-t) sage: f.full_simplify() 1/2*log(2) In my session, I had the difference of two logarithms. In yours above, you've got the sum. Is that an actual sage session? I get something different on 4.8.alpha6: sage: f = (1/2)*log(2*t) + (1/2)*log(-t) sage: f.full_simplify() 1/2*I*pi + 1/2*log(2) + log(t) In the example below, with t=-1, both logs should have imaginary part pi and real parts log(2) and zero respectively? There's no global function for it, but what you want is to call full_simplify() on the expression. sage: f = (1/2)*log(2*t) - (1/2)*log(t) sage: f.full_simplify() 1/2*log(2) -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
