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From: SourceForge.net <noreply@so...>  20081130 22:03:05

Bugs item #1504146, was opened at 20060610 17:59 Message generated for change (Comment added) made by dgildea You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=1504146&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  Assume Group: None >Status: Closed >Resolution: Fixed Priority: 5 Private: No Submitted By: Stavros Macrakis (macrakis) >Assigned to: Dan Gildea (dgildea) Summary: taylor asks pn? when expr is zero Initial Comment: taylor( asin( ( cos(x+a)^2 + sin(x)^21 ) / a), a, 0, 2) asks whether sin(x)^2+cos(x)^21 is positive or negative, where of course it is identically zero.  >Comment By: Dan Gildea (dgildea) Date: 20081130 17:03 Message: as of comm2.lisp rev 1.22, simpatan2 no longer asks questions: (%i8) taylor( asin( ( cos(x+a)^2 + sin(x)^21 ) / a), a, 0, 2); (%o8) %i*log(a)+(log(abs(2*sin(x)^2+2*cos(x)^22))*%i +atan2(2*sin(x)^2+2*cos(x)^22,0)) +2*%i*cos(x)*sin(x)*a/(sin(x)^2+cos(x)^21) (4*%i*sin(x)^4+(8*%i*cos(x)^24*%i)*sin(x)^24*%i*cos(x)^4 +4*%i*cos(x)^2%i) *a^2 /(4*sin(x)^4+(8*cos(x)^28)*sin(x)^2+4*cos(x)^48*cos(x)^2+4) (%i9) trigsimp(%); atan2(0,0) has been generated. (oops)  Comment By: Stavros Macrakis (macrakis) Date: 20061118 14:52 Message: Logged In: YES user_id=588346 Originator: YES > Also, the graph (2d!) of sin(x)^2+cos(x)^2 is not a straight line! This is because of rounding errors. To see clearly how small these errors are, try plot2d(sin(x)^2+cos(x)^21,[x,0,6]); This gives you a useful scale for the y axis. Unfortunately, plot2d(sin(x)^2+cos(x)^2,...) does not  it shows the min and max values as 1, where it is in fact 0.999999999999999 > 1.000000000000001 or something.  Comment By: Nobody/Anonymous (nobody) Date: 20061118 11:16 Message: Logged In: NO Also, the graph (2d!) of sin(x)^2+cos(x)^2 is not a straight line! S.Sangwal sangwal77 AT yahoo.com  Comment By: Stavros Macrakis (macrakis) Date: 20060611 14:47 Message: Logged In: YES user_id=588346 It would be OK if taylor/asksign asked if the expression was pnz, because the user could answer z (there will always be some cases that asksign can't handle, after all). The problem is that taylor/asksign is asking if it is pn, not giving the user the possibility of answering z.  Comment By: Robert Dodier (robert_dodier) Date: 20060611 14:30 Message: Logged In: YES user_id=501686 I don't think the bug is in taylor; reassigning the category to "Lisp Core  Assume". Feel free to change the category again. asksign (sin(x)^2+cos(x)^21); => Is sin(x)^2+cos(x)^21 pnz ? is(equal(sin(x)^2+cos(x)^21,0)); => Maxima was unable to evaluate the predicate I don't know how hard asksign and/or is and/or mevalp should try to simplify. trigsimp(sin(x)^2+cos(x)^21); => 0 but trigsimp isn't applied automatically.  You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=1504146&group_id=4933 