Am 01.09.2014 um 13:28 schrieb F. B.:
SymPy's default pattern matcher is not a structural one, i.e. it tries to match according to some mathematical rules. A structural pattern matcher would instead just match the structure of the expression-tree.While it is necessary to have some mathematical awareness such as, give the wild *w*: - associativity awareness (i.e. f(a, b, c) = f(a, f(b, c)) and similar): (a+b+c).match(a+w) ==> {w: b+c} - commutativity awareness: (a+b).match(w+a) ==> {w: b} - one-identity awareness (f is one-identical if f(x) = x for any x): x.match(Add(w, evaluate=False)) ==> {w: x}
You can inject math awareness into a structural pattern matcher by letting the structure declare its mathematical properties.
E.g. a function could have a one_identity_aware attribute, and the structural pattern matcher could have a primitive that inspects such attributes.
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