Dan Gordon on Mon, 17 Apr 2000 14:47:12 -0700 (PDT) |
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padic multiplication bug |
I've run into an odd bug multiplying p-adic polynomials in newer versions of GP. Let f = (1 + O(2^20))*y^9 + (2^14 + O(2^34))*y^7 + (2^54 + O(2^74)) g = (1 + O(2^20))*y^12 + (2^92 + O(2^102)) The correct answer is: f*g = (1 + O(2^20))*y^21 + (2^14 + O(2^34))*y^19 + (2^54 + O(2^74))*y^12 + (2^92 + O(2^102))*y^9 + (2^106 + O(2^116))*y^7 + (2^146 + O(2^156)) In 2.0.19 (and versions at least as far back as 2.0.16), I get: f*g = (1 + O(2^20))*y^21 + (2^14 + O(2^34))*y^19 + O(2^20)*y^14 + O(2^34)*y^12 + (2^92 + O(2^102))*y^9 + (2^106 + O(2^116))*y^7 + (2^146 + O(2^156)) with wrong coefficients of y^14 and y^12. Can anyone tell me what's going on? By the way, I ran into this while implementing a new p-adic factoring routine. In version 2.0.10 and before, it was easy to find p-adic polynomials which factorpadic couldn't handle, such as (x-4)^2 * (x^2-2) + 2^100. With later versions, factorpadic easily handles this and other examples we had. Is there any documentation about what improvements have been made to factorpadic? Dan Gordon