       Re: Multiplying large polynomials

• To: mathgroup at smc.vnet.net
• Subject: [mg14712] Re: Multiplying large polynomials
• From: Rolf Mertig <rolf at mertig.com>
• Date: Tue, 10 Nov 1998 01:21:04 -0500
• Organization: Mertig Research & Consulting
• References: <7257a7\$88m@smc.vnet.net>
• 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.

--

In:=  poly1=a h^2+b + O[h]^3;

In:= poly2 = d h+e + O[h]^3;

In:=  poly1 poly2 // Normal //InputForm

Out//InputForm= b*e + b*d*h + a*e*h^2

Rolf Mertig

Mertig Research & Consulting
Mathematica training and programming Development and distribution of
FeynCalc  Amsterdam, The Netherlands
http://www.mertig.com

```

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