On Feb 2, 1:01 am, casevh <cas...@gmail.com> wrote: > On Feb 1, 10:02 pm, Mensanator <mensana...@aol.com> wrote: > > > > > > > On Feb 1, 8:20 pm, casevh <cas...@gmail.com> wrote: > > > > On Feb 1, 1:04 pm, Mensanator <mensana...@aol.com> wrote: > > > > > On Feb 1, 2:27 am, casevh <cas...@gmail.com> wrote: > > > > > > On Jan 31, 9:36 pm, "Tim Roberts" <t.robe...@cqu.edu.au> wrote: > > > > > > > Actually, all I'm interested in is whether the 100 digit numbers > > > > > > have an exact integral root, or not. At the moment, because of > > > > > > accuracy concerns, I'm doing something like > > > > > > > for root in powersp: > > > > > > nroot = round(bignum**(1.0/root)) > > > > > > if bignum==long(nroot)**root: > > > > > > ......... > > > > > > which is probably very inefficient, but I can't see anything > > > > > > better..... > > > > > > > Tim > > > > > > Take a look at gmpy and the is_power function. I think it will do > > > > > exactly what you want. > > > > > And the root function will give you the root AND tell you whether > > > > it was an integral root: > > > > > >>> gmpy.root(a,13) > > > > > (mpz(3221), 0) > > > > > In this case, it wasn't. > > > > I think the original poster wants to know if a large number has an > > > exact integral root for any exponent. is_power will give you an answer > > > to that question but won't tell you what the root or exponent is. Once > > > you know that the number is a perfect power, you can root to find the > > > root. > > > But how do you know what exponent to use? > > That's the gotcha. :) You still need to test all prime exponents until > you find the correct one. But it is much faster to use is_power to > check whether or not a number has representation as a**b and then try > all the possible exponents than to just try all the possible exponents > on all the numbers.
Ok. I was under the impression that the OP was only interested in the 13th root, so that is_power wouldn't necessarily be of any use to him. If is_power returned true, you would still have to do root(a,13) to see if it's actually a 13th power. That's executing two gmpy functions and takes twice as much time as doing root(a,13) alone. > > > > > > > > > >http://code.google.com/p/gmpy/ > > > > > > casevh -- http://mail.python.org/mailman/listinfo/python-list
