symmetric function

[danabe]

Hi all,

Is it possible to define a general symmetric function of two variables, let's say F(x,y) such that F(x,y)-F(y,x) would evaluate to zero?

Thanks

[Francesco Bonazzi]

Not in the functions, but there is a symmetry canonicalization algorithm in the tensor module:

http://docs.sympy.org/latest/modules/tensor/tensor.html

Unfortunately it's unrelated.

[Aaron Meurer]

The easiest way is to define a Function subclass that sorts the arguments.

class F(Function):
@classmethod
def eval(cls, x, y):
if default_sort_key(x) > default_sort_key(y):
return cls(y, x)

For more than two variables, I would use the algorithm described by Francesco.

Aaron Meurer

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