The following matrix operation produces wrong answer in online Sage: M=matrix(RR,[[7,3,10,13],[1,1,2,2],[1,2,3,4],[1,3,5,7]]);det(M);invM=M^(-1);invM*M;det(invM) If one changes RR to QQ the answers turn correct. Or it is enough to change one corner matrix entry to: M=matrix(RR,[[8,3,10,13],[1,1,2,2],[1,2,3,4],[1,3,5,7]]);det(M);invM=M^(-1);invM*M;det(invM) to get right answers. How can one be sure about Sage linear algebra w/this problem? Am I missing something obvious? It took me several hours to zero in on this bug from a large program. Ant feedback will be appreciated.
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