Hello, To do the symbolic differentiation, I created a new class, that store the dependencies with respect to a symbol (or many) and the degree of differentiation. Then I can differentiate the symbol (add 1 to the degree). and at the end I can make the substitution and the real differentiation. I'm not sure that is the correct approach, but it works for me. Felipe. Le 22 juil. 12 à 19:29, Martin Ettl a écrit :

Hello,

i have a question regarding symbolic differentiation with GiNAC.

Here is what i am trying to do:

I have to variables a(t) and b(t), both are dependent from time (t). Suppose, this two variables are multiplied liked this:

a(t) * b(t)

Is it possible to derive this expression (a(t)*b(t)) according time with ginac.

The only function i found in the manual is usefull for partial derivation, which does not help me here.

Here is some example code:

symbol a("a"), b("b"); // <-- how to tell ginac that variable a and b is dependant from variable t expression f = a*b; std::cout << f.diff(t,1) << std::endl;

Many thanks in advance and best regards

Martin Ettl

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Hi, On 22.07.2012 19:29, Martin Ettl wrote:

I have to variables a(t) and b(t), both are dependent from time (t). Suppose, this two variables are multiplied liked this:

a(t) * b(t)

Is it possible to derive this expression (a(t)*b(t)) according time with ginac.

yes, and like your notation already suggests, you need to define a and b as functions of t. A simple code example would be: #include <ginac/ginac.h> using namespace GiNaC; #include <iostream> using namespace std; DECLARE_FUNCTION_1P(a) DECLARE_FUNCTION_1P(b) REGISTER_FUNCTION(a, dummy()) REGISTER_FUNCTION(b, dummy()) int main() { symbol t("t"); ex expr = a(t) * b(t); cout << expr << endl; cout << expr.diff(t,1) << endl; return 0; } But you will get fderivative objects in the result (printed as something like D[0], because with dummy() in the function definition macro you have not told GiNaC what the partial derivative of a or b with respect to t is supposed to be. You can look in the tutorial in section 6.2.2 for a more elaborate example. Regards, Jens