Igor Schein on Fri, 11 Dec 1998 15:11:26 -0500 |
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roundoff(?) bug |
Hi, here's the problem: ? A=x^12+16; ? B=x^12+4*x^9+22*x^6+12*x^3+2; ? C=x^12-4*x^9+22*x^6-12*x^3+2; ? setsearch(Set(polred(B)),A) 2 ? setsearch(Set(polred(B)),C) 3 ? setsearch(Set(polredabs(A,4)),B) 2 ? setsearch(Set(polredabs(B,4)),C) 4 ? setsearch(Set(polredabs(A,4)),C) 0 First two setsearch() commands verify that all three polynomials define the same number field. The 3rd setsearch() command indicates that B has the same t2-norm as A. The 4th setsearch() command indicates that C has the same t2-norm as B. However, The 5th setsearch() command indicates that C *does not* have the same t2-norm as A. I'll allow myself to speculate that a round-off error occurred somewhere, probably during the polroots() stage. Thanks Igor