From: SourceForge.net <no...@so...> - 2011-12-08 15:14:24
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Bugs item #3443554, was opened at 2011-11-27 15:31 Message generated for change (Comment added) made by jensenripley You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=3443554&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: Lisp Core - Integration Group: None Status: Open Resolution: None Priority: 5 Private: No Submitted By: Ripley (jensenripley) Assigned to: Nobody/Anonymous (nobody) Summary: Tío different results for an integral Initial Comment: Hello, By integrating sqrt(4*x^2-y^2) into the triangle {0<x<1; 0<y<x} in two diffferent order: integrate( integrate( sqrt(4*x^2-y^2), x , y, 1), y , 0,1) Integrate( integrate( sqrt(4*x^2-y^2), y, 0, x), x, 0,1) WxMaxime give two different results. Where is the mistake? ---------------------------------------------------------------------- >Comment By: Ripley (jensenripley) Date: 2011-12-08 07:14 Message: I couldn't realize that is simply a mistake... So, should I assume Maxima integrator subroutines aren't trustworthy? I like Maxima but it is not admissible for me to work with a not trusty "scientific" software... Could someone give a hand to have any reference to how Maxima manage integrals internally? I am going to do my best to find the bug... ---------------------------------------------------------------------- Comment By: Raymond Toy (rtoy) Date: 2011-11-30 11:05 Message: I have looked very briefly at this. The intermediate indefinite integrals look right, and maxima says the derivative simplifies to the integrand, so I don't really know what's wrong. I think the thing to do is to examine whether the indefinite integrals are actually correct. There could be a problem with choosing the wrong branch since one of the integrals involves inverse trig functions. ---------------------------------------------------------------------- Comment By: jcvtrip (jcvtrip) Date: 2011-11-30 09:27 Message: Please, some help on this question? Any comment would be helpful... ---------------------------------------------------------------------- Comment By: jcvtrip (jcvtrip) Date: 2011-11-28 10:01 Message: Hello, Here you have a transcript... Maxima version: 5.25.1 Maxima build date: 9:14 9/5/2011 Host type: i686-apple-darwin10.8.0 Lisp implementation type: SBCL Lisp implementation version: 1.0.47 expres:sqrt(4*x^2-y^2); (%o5) sqrt(4*x^2-y^2) integrate(integrate(expres, x,y,1),y,0,1); "Is "y-1" positive, negative, or zero?"n; "Is "y" positive or negative?"p; (%o6) (3*log(4*sqrt(3)+8)+4*%pi-1)/18 ev(%o6,numer); (%o12) 1.093118188249627 integrate(integrate(expres, y, 0,x),x,0,1); "Is "x" positive, negative, or zero?"p; (%o10) (2*%pi+3^(3/2))/18 ev(%o10,numer); (%o13) .6377409849936787 ---------------------------------------------------------------------- Comment By: Ripley (jensenripley) Date: 2011-11-28 08:28 Message: Thank you rswarbrick but you mistaked the input line ( % i3)... You wrote Integrate(integrate(expr, x,0, x), x,0,1) instead of Integrate(integrate(expr, y, 0, x) ,x ,0,1) ---------------------------------------------------------------------- Comment By: Rupert Swarbrick (rswarbrick) Date: 2011-11-28 01:15 Message: Drat. I didn't realise that sourceforge would eat the text formatting. If it isn't clear, the first time I get an answer with logs and sqrts. The second time, I get a more complicated integrate noun form. ---------------------------------------------------------------------- Comment By: Rupert Swarbrick (rswarbrick) Date: 2011-11-28 01:13 Message: With a recent version of the sources, I get the following: Maxima 5.25post http://maxima.sourceforge.net using Lisp SBCL 1.0.53.0.debian Distributed under the GNU Public License. See the file COPYING. Dedicated to the memory of William Schelter. The function bug_report() provides bug reporting information. (%i1) expr: sqrt(4*x^2-y^2); 2 2 (%o1) sqrt(4 x - y ) (%i2) integrate(integrate(expr, x, y, 1), y, 0, 1); Is y - 1 positive, negative, or zero? n; Is y positive or negative? pos; 3 log(4 sqrt(3) + 8) + 4 %pi - 1 (%o2) -------------------------------- 18 (%i3) integrate(integrate(expr, x, 0, x), x, 0, 1); Is x positive, negative, or zero? pos; Is y positive or negative? pos; rat: replaced -1.e-8 by -1/100000000 = -1.e-8 <snip lots more rat warnings: eugh.> Is y positive or negative? pos; 1 / 2 2 2 2 [ y log(4 sqrt(4 x - y ) + 8 x) y log(4 %i y) (%o3) I (- ------------------------------- + -------------- ] 4 4 / 0 2 2 x sqrt(4 x - y ) + -----------------) dx 2 This, while unhelpful isn't wrong. Can you post a transcript of what you actually do and get (use maxima from the command line, maybe). Definitely include the version of Maxima that you're using. Rupert ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=3443554&group_id=4933 |