How to substitute certain function?

[zhaoli-IHEP]

For example

@vars a b x y

@funs f g

ex1 = f(a,b)

ex2 = subs( ex1, f(x_,y_), g(x_+y_) ) # maybe some wildcard for the arguments?

An alternative approach I can imagine is to iterate over the expression tree.
So I found there are functions "get_name" and "get_args".
However, it is not very clear for "get_name" to show the operation + and *

If neither above works, it seems I have to turn the expression into String and using regex to implement the substitution, but this lose the point to use SymEngine.

[isuruf]

What you can do right now is recursively call get_args on the expression and use get_name if the expression is a FunctionSymbol to create a dictionary for subs.
I agree that this is a useful thing to implement in the C++ library.

[zhaoli-IHEP]

What you can do right now is recursively call get_args on the expression and use get_name if the expression is a FunctionSymbol to create a dictionary for subs.
I agree that this is a useful thing to implement in the C++ library.

Thank you for your reply.
It could be an effective approach. However, how can I know if it is a FunctionSymbol?

[isuruf]

You can use get_symengine_class(x) == :FunctionSymbol

[zhaoli-IHEP]

You can use get_symengine_class(x) == :FunctionSymbol

Thank you!

[Myrddinlefou]

Hi zhaoli-IHEP,
did you code your recursive function ? I have the same type of problem and if you have an effective function I am very interesting.

Thank's a lot.

[zhaoli-IHEP]

Hi zhaoli-IHEP,
did you code your recursive function ? I have the same type of problem and if you have an effective function I am very interesting.

Thank's a lot.

Hi, in fact we did not make generic function to handle this problem. What we do is to use function_symbols to find all functions and then filter them and then make replacement subs for each specific instance.