Hello, it's me again.
I am trying to optimise small module for working with polynomials, and
I have encountered problem: new, optimised, code, doesn't work in some
specific case. Here's the old version of the code:
(3x^2 + 2x + 1 <=> poly([3, 2, 1]), btw)
def __add__(self, other):
"Return sum of two polynomials"
rcoefs1 = list(reversed(self.coefs))
rcoefs2 = list(reversed(other.coefs))
coefs = [c1+c2 for c1,c2 in zip(rcoefs1, rcoefs2)]
minlen = min(len(rcoefs1), len(rcoefs2))
coefs.extend(rcoefs1[minlen:] + rcoefs2[minlen:])
return Polynomial(reversed(coefs))
Here's the new version:
def __add__(self, other):
rcoefs1 = reversed(self.coefs)
rcoefs2 = reversed(other.coefs)
coefs = [c1+c2 for c1,c2 in it.izip(rcoefs1, rcoefs2)]
coefs.extend(it.chain(rcoefs1, rcoefs2)) #? -- here is magic
if coefs[-1] != 0:
return Polynomial(reversed(coefs), False, False)
else:
return Polynomial(reversed(coefs), False)
Last four lines are ok (tested), "magic" seems to occure in #? line.
What's the magic? Here it is:
poly([1,2,1]) + poly([1,-2,1]) is ok,
poly([1,-2,1]) + poly([5,4,3,2,1]) is ok,
poly([1]) + poly([2]) is ok,
poly([1,2,1]) + poly([5,4,3,2,1]) is ok, but
poly([1,0]) + poly([-1]) gives poly([-1]),
poly([1,-3]) + poly([-2]) gives poly([-5]) etc.
So, "magic" happens when processing something like poly([a,b]) +
poly([c]) and it gives poly([b+c]) as result. Can anybody help me with
it?
Regards, Gregory.
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