On May 2, 1:29 pm, someone <newsbo...@gmail.com> wrote: > > If your data starts off with only 1 or 2 digits of accuracy, as in your > > example, then the result is meaningless -- the accuracy will be 2-2 > > digits, or 0 -- *no* digits in the answer can be trusted to be accurate. > > I just solved a FEM eigenvalue problem where the condition number of the > mass and stiffness matrices was something like 1e6... Result looked good > to me... So I don't understand what you're saying about 10 = 1 or 2 > digits. I think my problem was accurate enough, though I don't know what > error with 1e6 in condition number, I should expect. How did you arrive > at 1 or 2 digits for cond(A)=10, if I may ask ?
As Steven pointed out earlier, it all depends on the precision you are dealing with. If you are just doing pure mathematical or numerical work with no real-world measurement error, then a condition number of 1e6 may be fine. But you had better be using "double precision" (64- bit) floating point numbers (which are the default in Python, of course). Those have approximately 12 digits of precision, so you are in good shape. Single-precision floats only have 6 or 7 digits of precision, so you'd be in trouble there. For any practical engineering or scientific work, I'd say that a condition number of 1e6 is very likely to be completely unacceptable. -- http://mail.python.org/mailman/listinfo/python-list
