Comment #2 on issue 980 by nicolas.pourcelot: log(8)/log(2) should
automatically simplify to 3
http://code.google.com/p/sympy/issues/detail?id=980
Similarly, ln(9)-2*ln(3), or ln(10)-ln(2)-ln(5) should return 0.
Maybe some log expansion would provide useful for simplification ; after
that log may
be gathered again.
Eg., for expansion, something like that :
def expand_log(expr):
if isinstance(expr, sympy.log) and expr.args[0].is_rational:
num, den = expr.args[0].as_numer_denom()
result = 0
for n, p in sympy.factorint(num):
result += p*sympy.log(n)
for n, p in sympy.factorint(den):
result -= p*sympy.log(n)
return result
elif expr.args:
return expr.func(*(expand_log(arg) for arg in expr.args))
else:
return expr
Collecting logs is a bit more difficult.
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