Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
Drexel University or The Math Forum.



Re: Problem with Expand and Modulus in Mathematica 9?
Posted:
Jan 2, 2013 9:14 PM


On Friday, December 28, 2012 4:33:15 AM UTC6, Ralf Hemmecke wrote: > 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
Hi Ralf,
Yes, this appears to be problematic, and I have has been reported in house.
For now a workaround is to first do:
SetSystemOptions[ "PolynomialAlgebraOptions" > {"PolynomialExpand" > False}];
Name notwithstanding, this should not actually disable expansion; it simply enables usage, or not, of a certain internal method.
I apologize for any problems this may have caused.
Daniel Lichtblau Wolfram Research



