Re: Q: D[EllipticK[k],k] ?
- To: mathgroup at christensen.cybernetics.net
- Subject: [mg2010] Re: Q: D[EllipticK[k],k] ?
- From: "Brian J. Albright" <albright at physics.ucla.edu>
- Date: Thu, 14 Sep 1995 23:27:57 -0400
- Organization: UCLA Department of Physics and Astronomy
"David O. Gunter" <david_gunter at qmgate.anl.gov> wrote: >I need to know if it's possible to obtain the derivative of the >complete elliptic integral given by EllipticK[k], where k is some >parameter. I've tried > D[EllipticK[k], k] >with the output result > EllipticK'[k] >and when I try > N[%] /. x->0.5 >I get > EllipticK'[0.5]. > > >How can I obtain the numerical answer this derivative? > >Thanks in advance. > >-david gunter > > You might try numerically approximating the derivative: In:= NEllipticK'[x_] = (EllipticK[x + eps] - EllipticK[x - eps])/(2 eps) + O[eps^3 EllipticK'''[x]] /. eps -> 0.00001; In:= NEllipticK'[0.5] -15 (3) Out:= 0.847213 + O[1. 10 EllipticK [0.5]] If the error in the derivative approx. is small enough for your purposes, you can get the approximate numerical value from: In:= Normal[%] Out:= 0.847213 Regards, -Brian -- Brian J. Albright Department of Physics and Astronomy, UCLA albright at physics.ucla.edu http://bohm.physics.ucla.edu/~albright