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## reduce-algebra-developers — Discussion of development, administration and support for Reduce

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 Re: [Reduce-algebra-developers] An inconsistency in computing derivatives? From: Rainer Schöpf - 2011-09-05 18:26:37 ```Well, there is a least one problem: -------------------------------- Reduce (Free PSL version), 5-Sep-2011 ... 1: let x^3=u; 2: df(x,u); df(x,u) 3: on expanddf; 4: df(x,u); ***** Segmentation Violation in diffp -------------------------------- This is from trying to take a cdr of nil, in the line reading if !*expanddf and not(v memq (x:=cdr atsoc(u, depl!*))) then << It happens when u (in this case the symbol x) can be found in powlis!* but not in depl!*. I think that the chain rule shouldn't be applied here, ie. the code should read something like (at the same time protecting against cdr nil): if !*expanddf and (not (x:= atsoc(u,powlis!*)) or not depends(cadddr x,v)) and not (x := atsoc(u, depl!*) and (v memq (x := cdr x))) then << Rainer __________________________________________________________________________ On Fri, 2 Sep 2011 at 18:22 +0100, Francis Wright wrote: > I think this is code that I had a hand in a while ago and I think I didn?t > consider the case of mixed explicit and implicit dependence. I agree that > this case should be included. I think I regarded this code as experimental, > which is probably why it didn?t get put into the manual. Given that the code > is still there it can't have caused undue problems, so it's probably time it > was included in the manual! > > Francis > > > -----Original Message----- > > From: Rainer Schöpf [mailto:rainer.schoepf@...] > > Sent: 01 September 2011 6:21 pm > > To: reduce-algebra-developers@... > > Subject: [Reduce-algebra-developers] An inconsistency in computing > > derivatives? > > > > Compare the following examples > > > > A) > > -------------------------------- > > 1: depend f,r; > > > > 2: depend r,x; > > > > 3: df(f,x); > > > > df(f,x) > > > > 4: on expanddf; > > > > 5: df(f,x); > > > > df(f,r)*df(r,x) > > -------------------------------- > > > > B) > > -------------------------------- > > 1: operator f; > > > > 2: depend r,x; > > > > 3: df(f(r),x); > > > > df(f(r),x) > > > > 4: on expanddf; > > > > 5: df(f(r),x); > > > > df(f(r),x) > > -------------------------------- > > > > With on expanddf, the chain rule is applied to the first example, but not > to the > > second one. Shouldn't this be done as well? > > > > The second one is needed for the changevr package; this package redefines > diffp > > to achieve it. > > > > (As an aside: the new switches like expanddf are not described in the > manual; > > was this deliberate? If not, I'll update the documentation.) > > > > Rainer > > > > > ---------------------------------------------------------------------------- > -- > > Special Offer -- Download ArcSight Logger for FREE! > > Finally, a world-class log management solution at an even better > price-free! And > > you'll get a free "Love Thy Logs" t-shirt when you download Logger. Secure > your > > free ArcSight Logger TODAY! > > http://p.sf.net/sfu/arcsisghtdev2dev > > _______________________________________________ > > Reduce-algebra-developers mailing list > > Reduce-algebra-developers@... > > https://lists.sourceforge.net/lists/listinfo/reduce-algebra-developers > ```

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