On Fri, Jun 10, 2011 at 9:33 AM, Craig DeForest <[email protected]> wrote: > Hmmm... I wonder if we should have inv report this condition > (a noninvertible or quasi-noninvertible input)...
Sounds like a good idea. If we use the det() method with the option to cache the results of the LU decomposition we'll have hardly any performance penalty. Then just a check against an appropriate value for machine epsilon. --Chris > On Jun 10, 2011, at 7:14 AM, Chris Marshall wrote: > >> You matrix is not invertible which is why the first >> answer comes out funny. The matrix inverse routine >> does not do checking for condition numbers, etc >> before it calculates the inverse. If you print the >> determinant you'll see it is very small (i.e. floating >> point zero within round-off). >> >> The reason your cut and paste "check" worked >> is because you only included the top several places >> from the sprint of the numbers which is enough to >> make the determinant farther from 0 and the matrix >> then invertible. It is not actually inverting the >> same matrix.... >> >> --Chris _______________________________________________ Perldl mailing list [email protected] http://mailman.jach.hawaii.edu/mailman/listinfo/perldl
