Re: Multiplying large polynomials

*To*: mathgroup at smc.vnet.net*Subject*: [mg14719] Re: [mg14685] Multiplying large polynomials*From*: Carl Woll <carlw at fermi.phys.washington.edu>*Date*: Tue, 10 Nov 1998 01:21:09 -0500*Sender*: owner-wri-mathgroup at wolfram.com

Hi Thomas, This looks like a good application for Series. poly1 = a h^2 + b; poly2 = d h + e; N = 2; s1 = poly1 + O[h]^3; s2 = poly2 + O[h]^3; s1 s2 should return something like b e + b d h + a e h^2 + O[h]^3 Carl Woll Dept of Physics U of Washington On Sun, 8 Nov 1998, Thomas Bell wrote: > I'm trying to multiply two huge polynomials, and memory is a major > concern. I want to truncate the resulting polynomial to a specified > power (N) in one of the variables (h), and I was wondering if it was > possible to tell Mathematica to not bother multiplying two terms if the > resulting power of h was greater than N. This is, of course, in the > hope that this "automatic truncation" would save time and memory. For > example, if > > poly1 = a h^2 + b; > poly2 = d h + e; > N = 2; > > then I would like to result to be > > result = a e h^2 + b d h + b e > > Instead, I have to write > > result = Expand[poly1 poly2]/.h^3 -> 0; > > which forces Mathematica to create the enormous product before > truncating. Please cc to tombell at stanford.edu, and thanks in advance > for any suggestions. > >