[GiNaC-list] setting and getting numeric values from indexed expressions

Alejandro Limache alejandrolimache at hotmail.com
Fri Jul 28 03:02:36 CEST 2006

Hello people,
I have the following question.
Is there a way to SET and GET numeric values from indexed expressions?

Consider the 2 following cases:

1) For matrices. In the tutorial Section 4.13 one sees that is possible to 
         matrix A(2, 2), B(2, 2), C(2, 2);
         A =  1, 2,
              3, 4;
         B = -1, 0,
              2, 1;
         C =  8, 4,
              2, 1;
         e = indexed(A, i, k) * indexed(B, k, j) - 2 * indexed(C, i, j);
         cout << e.simplify_indexed() << endl;
          // -> [[-13,-6],[1,2]].i.j
Is there a way to get the numeric values of each of the components of e?
I would like to be able to do something like
         double d;
         d = e(0,0);
to get:

2) Can something similar be done for indexed expression not defined as 
For example given something like
         symbol  A("A")....
         idx i(.., 3), j(.., 3), k(..,10);
         ex e = indexed(A,i,j,k)
could I set for example: i=2, j=0, k=4 and set A(2,0,4)=3.5 ?
could I then somehow get the value "3.5" back?

Thank you for your help!

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