Comment #43 on issue 2607 by smi...@gmail.com: as_numer_denom() is too slow
http://code.google.com/p/sympy/issues/detail?id=2607
I'm finding that there are too many special things to watch out for.
The approach is sound, I think, but what is going to happen is that I
am just going to end up re-writing Mul's flatten machinery. What we
need is a way to keep all the flatten info and then just update that
info as terms are removed.
Here's the basic approach I am taking;
calc num, den of all terms
if all dens are the same, return Add(*nums), den[0]
find lcm of den coeffs
multiply num_i by lcm/den_i's coeff and remove den_i's coeff [so
all dens become coeff free]
collect common dens and update nums, e.g. num, den = [1, 3*y], [x,
x] -> [1 + 3*y], [x]
if all dens are the same, return Add(*nums), den[0]
numden = Mul(*(num+den))
terms = []
for i in range(len(num)):
term = divide(numden, num[i])
for j in range(len(num)):
if j == i: continue
term = divide(term, den[j])
terms.append(term)
for j in range(len(num)):
numden = divide(numden, den[j])
return Add(*terms), numden
All the details are in the divide routine (which doesn't exist
separate from my asnd routine). That's what we need to do the
efficient processing because all the terms are present, so we are
either going to be totally removing a term (divide(x*y, x)) or
updating a term (divide(x**2*y, x)). The order of the terms isn't
going to change so we can just rebuild the mul with new_rawargs. The
problem right now are the 'orphans', things that changed appearance
when multiplied together, e.g. 2**x*2**x -> 4**x so when you try
divide by 2**x, that term isn't found. The same for things like I and
radicals.
btw, something interesting I noticed is that in testing 4b, `den*n/d`
was faster than `den/d*n` and I'm not sure why.
--
You received this message because you are subscribed to the Google Groups
"sympy-issues" group.
To post to this group, send email to sympy-issues@googlegroups.com.
To unsubscribe from this group, send email to
sympy-issues+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sympy-issues?hl=en.
