I've been trying to use sympy.Symbol to implement a system where the
numerical value of a symbolic quantity is only fixed when it is evaluated
using evalf().
To accomplish this I've redefined _eval_evalf() to return the
aforementioned value (a fixed 5.0 in the toy example below).
This works fine with basic algebraic operations and most SymPy functions.
However, for some reason atan2 seems to behave differently and _eval_evalf
is never called.
Is this a bug, or have I misunderstood the purpose of _eval_evalf?
import sympy
import sympy.functions as syf
class A(sympy.Symbol):
def _eval_evalf(self, prec):
print('*')
return sympy.Float(5.0)
x = A('X')
y = A('Y')
print('polynomial:')
print((2*x-4+y).evalf()) # works fine
print('atan:')
print(syf.atan(y / x).evalf()) # works fine
print('beta:')
print(syf.beta(y, x).evalf()) # works fine
print('atan2:')
print(syf.atan2(y, x).evalf()) # prints "atan2(Y, X)", does not call
A._eval_evalf
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