RE: Multiplying large polynomials

*To*: mathgroup at smc.vnet.net*Subject*: [mg14710] RE: [mg14685] Multiplying large polynomials*From*: "Ersek, Ted R" <ErsekTR at navair.navy.mil>*Date*: Tue, 10 Nov 1998 01:21:02 -0500*Sender*: owner-wri-mathgroup at wolfram.com

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. > This should do it: In[4]:= Series[poly1*poly2,{h,0,2}]//Normal Out[4]//InputForm= b*e + b*d*h + a*e*h^2 I used InputForm for default output. Cheers, Ted Ersek