I have a script that generates a bunch of locally isomorphic quadratic forms and then tests them for global isometry. This script is too slow. Looking at profiling data much of the runtime is spent in the Quadratic forms class computing the useless local invariants and very little in the Pari qfisom calls. What can I do to cut down on this overhead?
So I solved the problem by going straight to Pari's qfisom routine that the is_globally_isomorphic routine eventually calls. The script generates the p-neighbors and checks for isometry, so all the forms are positive definite, but determining this is extremely expensive as currently implemented and overshadows the cost of the isomorphism testing.
To do this if $q1$ and $q2$ are the Gram matricies I write:
T = g1.__pari()__.qfisom(g2.__pari__())
and T is either False or the transformation matrix I want.
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For instance, typing
To do this, if `g_1` and `g_2` are the Gram matrices, I write:
T = g1.__pari()__.qfisom(g2.__pari__())
and `T` is either `False` or the transformation matrix I want.
will produce:
To do this, if
q_1andq_2are the Gram matrices, I write:T = g1.__pari()__.qfisom(g2.__pari__())and
Tis eitherFalseor the transformation matrix I want.
Asked: 2017-12-05 22:22:06 +0100
Seen: 321 times
Last updated: Dec 08 '17
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It will be hard to answer without more information. Could you tell more about the contents script ?