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March 2012

5 participants
2 discussions

Number representation
by Michel Dupront 29 Mar '12

29 Mar '12

Hello, I am new to ginac. At the moment I am playing with the tool trying to compute finite element bases as in SyFi. As a solution of a system of linear equations I got: {b0_0==0.25,b0_1==-0.25,b0_2==-0.25,b0_3==0.25} But I would have wanted the fraction 1/4 instead of 0.25. How can I force ginac to not compute fractions ? Thank in advance.

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converting expressions to double
by Tomasz I. Rudny 02 Mar '12

02 Mar '12

Hello, Thank you for GiNaC and your support - I have almost completed my PhD with it :) But I have a little problem still... I have a symbolic expression F(x, y, z, u) and I need to 1) substitute x, y, z, u with values (given as double), 2) calculate F, 3) export F as double. My code looks like this: double my_method(GiNaC::ex & ex, double x1, double y1, double z1, double u1) { numeric _x(x1), _y(y1), _z(z1), _u(u1); ex = ex.subs(lst(x == _x, y == _y, z == _z, u == _u)); ex = ex.evalf(); numeric tmp = ex_to<numeric>(ex); return tmp.to_double(); } Unfortunately, the last instruction (to_double() ) fails and throws the exception: terminate called after throwing an instance of 'cln::notreached_exception' what(): Internal error: statement in file real/conv/cl_R_to_double.cc, line 55 has been reached!! Please send the authors of the program a description how you produced this error! I read the response cited below, but still I can't fix it. Could you please help me? Thank you very much, Tomasz. Warsaw University of Technology ========================= Hi! On 11/02/2010 08:12 AM, Sebastian Luther wrote: > below you'll find a small test program that crashes for me. > > -------------------------------------------- > #include<ginac/ginac.h> > #include<iostream> > > int main(int argc, char* argv[]) > { > GiNaC::parser p; > GiNaC::ex e = p("941480149401/1250000000000000*2^(5/91)"); > GiNaC::numeric n = GiNaC::ex_to<GiNaC::numeric>(e); > double x = n.to_double(); //throws the exception below > return 0; > } Since e is a product (of a rational number and a power of two) it must be converted to a number using evalf() before trying to assign it to a simple numeric object. > Looks like the real problem lays in cln, but I'm not sure how to reproduce it there. It has nothing to do with CLN. Best wishes -richy. -- Richard B. Kreckel <http://www.ginac.de/~kreckel/>

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