September 2010 - GiNaC-list

get_name() doesn't returned a name like "symbolNNN"?
by Warren Weckesser 09 Dec '10

09 Dec '10

Hi, According to the documentation (section 4.5 of the online tutorial), the following code should produce something like z.get_name() = "symbol1" but with ginac 1.5.8, I get an empty string. ----- #include <iostream> #include <ginac/ginac.h> using namespace std; using namespace GiNaC; int main() { symbol z; cout << "z.get_name() = \"" << z.get_name() << "\"" << endl; return 0; } ----- In an older version of ginac, this used to work as documented. Is this a bug, or an expected change in behavior? (Or is it just my installation that is broken?) Regards, Warren

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archiving custom functions
by grey_earl＠web.de 11 Oct '10

11 Oct '10

Hello all, I was trying to archive custom functions (functions done with the macros as detailed in the tutorial, archiving also as in the tutorial). Archiving works fine, viewing the archives with viewgar -d gives me a complete output, without the -d switch viewgar complains about a non-existent function (logically!). When I try to read them in, however, I get a segmentation fault. Therefore my question: do I have to do anything special to make this work, or could it be a bug in the compiler? (which I cannot change, unfortunatly) Thanks ___________________________________________________________ Neu: WEB.DE De-Mail - Einfach wie E-Mail, sicher wie ein Brief! Jetzt De-Mail-Adresse reservieren: https://produkte.web.de/go/demail02

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open interval class with GiNaC's term evaluation engine
by Ulrich Loup 30 Sep '10

30 Sep '10

Hi, I try to implement a class for open intervals with interval arithmetic. I followed the instructions written in the GiNaC tutorial (6.5) and also used the implementation of "numeric" etc. as example code in order to get a clue of implementing the operators for my interval class. My goal is to get the class working with GiNaC's term evaluation engine and in particular, allow for polynomials with interval coefficients, which are automatically simplified by the use of the arithmetic operations I implemented. After several trials and errors I implemented a class which should, as I understood GiNaC's structure so far, work as expected - but it does not. I'm now not quite sure what I should concentrate on next or what I misunderstood. Could you give me a hint if it doesn't take you too much time? For further reading I attached, as an example, the open interval class files. I implemented the arithmetic operators in a separate file, just like it is in GiNaC itself. Regards, Ulrich.

2 1

unevaluated add in the result of imag_form()
by Burcin Erocal 25 Sep '10

25 Sep '10

Hi again, While looking into a problem in numerical evaluation in pynac, I ran into the following: ginsh - GiNaC Interactive Shell (ginac V1.5.7) <snip> Type ?? for a list of help topics. > a=(sqrt(4*(sqrt(3) - 5)*(sqrt(3) + 5) + 48) + 4*sqrt(3))/ (sqrt(3) + > 5); (sqrt(48+4*(5+sqrt(3))*(-5+sqrt(3)))+4*sqrt(3))*(5+sqrt(3))^(-1) > imag_part(a); (5+sqrt(3))^(-1)*sqrt(abs(48+4*(5+sqrt(3))*(-5+sqrt(3))))*sin(1/2*atan2(0,48+4*(-22))) Note that the second argument of atan2 is an add object in a rather unusual form: 48+4*(-22) Is this intended behavior? Thanks. Burcin

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same expression prints in differs orders
by Jose Antonio Garcia Peiro 21 Sep '10

21 Sep '10

>Hello, >On Tue, Sep 21, 2010 at 12:01 AM, Jose Antonio Garcia Peiro ><jgpeiro at gmail.com <https://www.cebix.net/mailman/listinfo/ginac-list>> wrote: >>* I think that the problem is at internal representation or at internal order. When*>>* I debug the code, same expression prints differ.*>>* ex test = pow(log(x),2)/x;*>>* cout << test;*>>* // sometimes x^(-1)*log(x)^2*>>* // other sometimes log(x)^2*x^(-1)* >Works as designed. This behavior is documented in the manual >(section 5.7.2, titled as 'Expanding and collecting'): "Again, >since the canonical form in GiNaC is not easy to guess you >should be prepared to see different orderings of terms in such >sums!". Also it has been explained on this mailing list several >(quite a number, actually) times, see e.g. > http://www.cebix.net/pipermail/ginac-list/2010-April/001598.html > h <http://www.ginac.de/pipermail/ginac-list/2008-August/001403.html>ttp://www.ginac.de/pipermail/ginac-list/2008-August/001403.html <http://www.ginac.de/pipermail/ginac-list/2008-August/001403.html> >>* How I can force GiNaC to unique representation?* >You can't. And there's no need to do so. Instead fix the (buggy) >code which makes assuptions about term ordering. >>* I am try to test expressions with "match", but it not works*>>* always with the same expression.* >Could you please post the actual expression and the pattern, >so I can make a (more) specific suggestion? >Best regards, > Alexei >You can't. And there's no need to do so. Instead fix the (buggy) >code which makes assuptions about term ordering. *mmm, I write about 50 lines with these assumptions, and i think that is not easy to correct....:-(* * * * >Could you please post the actual expression and the pattern, >so I can make a (more) specific suggestion? The code try to find the integral of a function. The code include all basic integration rules, for the function log(x)^2*x^(-1) apply these rule. ex f = pow(log(x),2)/x; // case a: f = x^(-1)*log(x)^2, case b: log(x)^2* x^(-1) * *ex w0, w1, w2;* *exmap m;* * * *if( f.match( pow(wild(0),wild(1))*wild(2), m ) || f.match( pow(wild(0),wild(1)), m ) ){ **// int( f^c*f', x) = f^(c+1)/(c+1) or ln(f) if c == -1* * w2 = 1; for( exmap::const_iterator i=m.begin(); i!=m.end(); ++i){ if (i->first.is_equal(wild(0)) ) w0 = i->second; // f else if (i->first.is_equal(wild(1)) ) w1 = i->second; // c else if (i->first.is_equal(wild(2)) ) w2 = i->second; // f' } if( has(w0,x) && !has(w1,x) ){ // f depends on x and c is constant ex dw0 = w0.diff(x,1); if( !dw0.is_equal(0) ){ // prevents division by 0 if( !has(w2/dw0,x) ){ if( w1.is_equal(-1) ){ //check if c == -1 return log( w0 ) * (w2/dw0); }else{ return pow( w0, w1+1 )/(w1+1) * (w2/dw0); } } } } } * * * *In case a: f = x, c = -1, and f' = log(x)^2, the code cannot compute the integral because f'/df = w2/dw0 = (log(x)^2)/(-x^-2) has the term 'x' and it cannot move out of integral.* *In case b: f = log(x), c = 2, f' = x^(-1), the code can compute integral because f'/df = w2/dw0 = x^(-1)/x^(-1) do not have the term 'x' and it can move out of integral.* The code fails because I assume that the product w2 dont have powers.

2 1

same expression prints in differs orders
by Jose Antonio Garcia Peiro 21 Sep '10

21 Sep '10

Hi, I am try to test expressions with "match", but it not works always with the same expression. I think that the problem is at internal representation or at internal order. When I debug the code, same expression prints differ. ex test = pow(log(x),2)/x; cout << test; // sometimes x^(-1)*log(x)^2 // other sometimes log(x)^2*x^(-1) How I can force GiNaC to unique representation? thanks

2 1

coeff() method
by Burcin Erocal 19 Sep '10

19 Sep '10

Hi, The following problem was reported to the Sage bug tracker by Paul Zimmermann: http://trac.sagemath.org/sage_trac/ticket/9505 ginsh - GiNaC Interactive Shell (ginac V1.5.7) <snip> Type ?? for a list of help topics. > f = x*y*z^2; y*z^2*x > coeff(f, z^2,1); y*x > coeff(f, x*y,1); 0 I'd greatly appreciate any help fixing this. Cheers, Burcin

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Fw: [sage-support] (5-e^x).substitute(x=log(x)) goes wrong?
by Burcin Erocal 19 Sep '10

19 Sep '10

Hi, This was reported to the sage-support list. I was intending to CC ginac-list in my reply, but hit send a bit too soon. Cheers, Burcin Begin forwarded message: On Fri, 10 Sep 2010 08:10:45 -0700 (PDT) KvS <keesvanschaik(a)gmail.com> wrote: > Dear all, > > I'm sorry I have yet again something to bother you with. Running the > following few lines: > > eq=5-e^x > print "1:",eq.substitute(x=3*x) > print "2:",eq.substitute(x=log(x)) > > yields the output (Sage 4.5.2 with Ubuntu): > > 1: -e^(3*x) + 5 > 2: -log(x) + 5 > > So 1 is fine, but it seems that to get to 2 Sage actually substitutes > twice no: 5-e^x -> 5-x -> 5-log(x). I had expected it would just give > me 5-x rather, is it a bug or a feature? Thanks for reporting the problem. This looks like a bug in GiNaC, the library we use for the symbolic expressions. ginsh - GiNaC Interactive Shell (ginac V1.5.7) __, _______ Copyright (C) 1999-2010 Johannes Gutenberg University Mainz, (__) * | Germany. This is free software with ABSOLUTELY NO WARRANTY. ._) i N a C | You are welcome to redistribute it under certain conditions. <-------------' For details type `warranty;'. Type ?? for a list of help topics. > subs(5-exp(x),x==log(x)); 5-log(x) I opened a ticket for this: http://trac.sagemath.org/sage_trac/ticket/9891

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using an "undefined" function
by Jose Antonio Garcia Peiro 09 Sep '10

09 Sep '10

Hi, I try to use an undefined function, such as f(x), instead of f(x)=3*x+... I know that the function depends on variable x, but not in what form. With SymbolicC++, if I define Symbolic x("x"), f[x] and g[x], the operation diff( f+g ,x ) returns diff(f,x)+diff(g,x). (the differentiation rule of sum operator) It is possible to make this with GiNaC? Thanks

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