## maxima-bugs

 [Maxima-bugs] [ maxima-Bugs-2921946 ] Expansion of bessel_k(1/2, x) with radexpand:false From: SourceForge.net - 2009-12-27 18:42:01 ```Bugs item #2921946, was opened at 2009-12-27 19:42 Message generated for change (Tracker Item Submitted) made by crategus You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=2921946&group_id=4933 Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: None Group: None Status: Open Resolution: None Priority: 5 Private: No Submitted By: Dieter Kaiser (crategus) Assigned to: Nobody/Anonymous (nobody) Summary: Expansion of bessel_k(1/2,x) with radexpand:false Initial Comment: The correct result for the expansion of bessel_k(1/2,x) is sqrt(%pi/2)*exp(-x)/sqrt(x) We get this result with Maxima too: (%i4) bessel_k(1/2,x),besselexpand:true; (%o4) sqrt(%pi)*%e^-x/(sqrt(2)*sqrt(x)) All seems to be correct, but this is by accident, because Maxima does in general the wrong simplification sqrt(1/x) -> 1/sqrt(x). We can see it, when we set the flag radexpand to false: (%i6) bessel_k(1/2,x),besselexpand:true,radexpand:false; (%o6) sqrt(%pi/(2*x))*%e^-x Now we get a result with sqrt(1/x) and not 1/sqrt(x), because the simplification sqrt(1/x) -> 1/sqrt(x) is switched off. If we evaluate the last expression for negative real numbers, we get a wrong sign. Dieter Kaiser ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=2921946&group_id=4933 ```
 [Maxima-bugs] [ maxima-Bugs-2921946 ] Expansion of bessel_k(1/2, x) with radexpand:false From: SourceForge.net - 2009-12-29 00:37:08 ```Bugs item #2921946, was opened at 2009-12-27 19:42 Message generated for change (Comment added) made by crategus You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=2921946&group_id=4933 Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: None Group: None >Status: Closed >Resolution: Fixed Priority: 5 Private: No Submitted By: Dieter Kaiser (crategus) Assigned to: Nobody/Anonymous (nobody) Summary: Expansion of bessel_k(1/2,x) with radexpand:false Initial Comment: The correct result for the expansion of bessel_k(1/2,x) is sqrt(%pi/2)*exp(-x)/sqrt(x) We get this result with Maxima too: (%i4) bessel_k(1/2,x),besselexpand:true; (%o4) sqrt(%pi)*%e^-x/(sqrt(2)*sqrt(x)) All seems to be correct, but this is by accident, because Maxima does in general the wrong simplification sqrt(1/x) -> 1/sqrt(x). We can see it, when we set the flag radexpand to false: (%i6) bessel_k(1/2,x),besselexpand:true,radexpand:false; (%o6) sqrt(%pi/(2*x))*%e^-x Now we get a result with sqrt(1/x) and not 1/sqrt(x), because the simplification sqrt(1/x) -> 1/sqrt(x) is switched off. If we evaluate the last expression for negative real numbers, we get a wrong sign. Dieter Kaiser ---------------------------------------------------------------------- >Comment By: Dieter Kaiser (crategus) Date: 2009-12-29 01:37 Message: Fixed in bessel.lisp revision 1.84. Closing this bug report as fixed. Dieter Kaiser ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=2921946&group_id=4933 ```