Hello Dr. Kisil,

The question from C. Trophime is not about evaluating the function but to define it.
​ Feel++ is a Finite Element library that main goal is to solve the variational problem a(u,v)=f(v) that arises from a lot of physical problems.

​We use GiNaC to dynamically define the right hand side of our problem, or our boundaries conditions and whatever can be expressed with it.

The question - I guess - can be explained like that​ :
I would like to define

• ​f(x) = 2*x if x>0

• f(x) = 3*x if x<=0.

Thus, basically, I would like to write

ex MyEx = (x<=0)?3*x:2*x

To my best knowledge, boolean expression are not handled in GiNaC, isn’t it ?

all the best,

Vincent H.