---------- Forwarded message ----------
From: Christian Szegedy <christian.szeg...@gmail.com>
Date: Thu, Dec 17, 2009 at 12:26 AM
Subject: sage bug report
To: William Stein <wst...@gmail.com>
Simple 8X8 matrix determinant computation makes sage hang:
load x.py
test()
On the other hand if m.det() is replaced m.inverse(), it runs through
in no time.
The determinant of the matrix is a sum of two monomials:
x1*x4*x5*x6 + x0*x2*x3*x7, but even the most primitive implementation
(summing all 8! permutations,most of them zero) should run through in
much less than minute.
--
William Stein
Associate Professor of Mathematics
University of Washington
http://wstein.org
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def genVar(i):
return "x%i"%i
def matrix_from_hash(h):
R=FractionField(PolynomialRing(GF(2),",".join(map(genVar,range(0,10)))))
h2 = {}
for p in h:
x=R.zero_element()
for v in h[p]:
x=x+R.gens()[v]
h2[p] = x
h2[p[1],p[0]] = x
return matrix(h2,sparse=False)
def test():
m = matrix_from_hash({(0, 1): [0, 5], (1, 2): [0], (5, 6): [2], (6, 7): [1], (4, 5): [4], (0, 7): [1, 7], (0, 6): [2, 1], (0, 5): [4, 2], (0, 4): [3, 4], (2, 3): [6], (0, 3): [6, 3], (3, 4): [3], (0, 2): [0, 6]})
print m
print(m.inverse())
