Dear Vladimir,

first of all thanks for your reply.

Well, defining the function as a GiNaC expression is part of my doubt, since I do not know how to represent the second-order
tensor E in GiNaC, and consequently, how to differentiate Psi with respect to it.

I've seen some classes for special tensors, like clifford, delta, etc, but it is not clear for me how to represent a second order tensor. I was guess I should use matrix and idx....but how? and how do I use diff afterwards?

Many thanks in advance.

Best regards,
Bernardo M. Rocha


2011/2/10 Vladimir V. Kisil <kisilv@maths.leeds.ac.uk>
               Dear Bernardo,

>>>>> On Wed, 9 Feb 2011 10:07:51 -0200, Bernardo Rocha <bernardosk@gmail.com> said:
   BMR> the strain energy function for the St. Venant-Kirchhoff
   BMR> material
   BMR> \Psi(E) = 0.5 * \lambda * (tr E)^2 + \mu E:E

       To start with, can you write this functions as a GiNaC expression?

       Best wishes,
       Vladimir
--
Vladimir V. Kisil     email: kisilv@maths.leeds.ac.uk
--                      www: http://www.maths.leeds.ac.uk/~kisilv/