Date: Dec 28, 2012 5:33 AM
Author: hemmecke
Subject: Problem with Expand and Modulus in Mathematica 9?

Can someone confirm that the following code gives different results for r1 for different versions of Mathematica and different operating systems. Or is this just an issue of my installation?

---BEGIN CODE---
m = 2147483629
q = -285170499
q1 = 1/q
q2 = PowerMod[q,-1,m]
Mod[q*q2, m]
p1 = 527660967 + 978421595*n
p2 = 1999783961 + 1587123368*n + 1965760814*n^2
r1 = Expand[q1*p1*p2,Modulus->m]
r2 = Expand[q2*p1*p2,Modulus->m]
s1 = Expand[Expand[q1*p1*p2],Modulus->m]
s2 = Expand[Expand[q2*p1*p2],Modulus->m]
---END CODE

Value of r1
Mathematica 8
1808010833 + 1914426603*n + 640234431*n^2 + 1087084730*n^3

Mathematica 9 (64bit Debian 6.0)
1651432217 + 309632549*n + 188919829*n^2 + 1597920481*n^3

Mathematica 9 (32bit Debian 6.0, 64bit CPU)
1823075307 + 33175446*n + 2081129601*n^2 + 580053941*n^3

The values of r2, s1, s2 agree with that of r1 as computed in Mathematica 8.

Ralf