I get slightly different results when I repeat a calculation. I've seen this problem before (it went away but has returned):
http://projects.scipy.org/pipermail/numpy-discussion/2007-January/025724.html A unit test is attached. It contains three tests: In test1, I construct matrices x and y and then repeatedly calculate z = calc(x,y). The result z is the same every time. So this test passes. In test2, I construct matrices x and y each time before calculating z = calc(x,y). Sometimes z is slightly different. But the x's test to be equal and so do the y's. This test fails (on Debian Lenny, Core 2 Duo, with libatlas3gf-sse2 but not with libatlas3gf-sse). test3 is the same as test2 but I calculate z like this: z = calc(100*x,y) / (100 * 100). This test passes. I get: ====================================================================== FAIL: repeatability #2 ---------------------------------------------------------------------- Traceback (most recent call last): File "/home/[snip]/test/repeat_test.py", line 73, in test_repeat_2 self.assert_(result, msg) AssertionError: Max difference = 2.04946e-16 ---------------------------------------------------------------------- Should a unit test like this be added to numpy?
"""Unit tests for repeatability. The problem and possible causes are discussed in the following thread: http://projects.scipy.org/pipermail/numpy-discussion/2007-January/025724.html If the tests do no pass, then try removing ATLAS-SSE2 from your system. But similar problems (not tested) may occur unless you remove all versions of ATLAS (SSE and BASE, for example). """ import unittest import numpy.matlib as M M.seterr(divide='ignore') M.seterr(invalid='ignore') def calc(x, y): return x * (x.T * y) def load(): # x data x = M.zeros((3,3)) x[0,0] = 0.00301404794991108 x[0,1] = 0.00264742266711118 x[0,2] = -0.00112705028731085 x[1,0] = 0.0228605377994491 x[1,1] = 0.00337153112741583 x[1,2] = -0.00823674912992519 x[2,0] = 0.00447839875836716 x[2,1] = 0.00274880280576514 x[2,2] = -0.00161133933606597 # y data y = M.zeros((3,1)) y[0,0] = 0.000885398 y[1,0] = 0.00667193 y[2,0] = 0.000324727 return x, y class Test_repeat(unittest.TestCase): "Test repeatability" def setUp(self): self.nsim = 100 self.x, self.y = load() def test_repeat_1(self): "repeatability #1" z0 = calc(self.x, self.y) msg = '' result = True for i in xrange(self.nsim): z = calc(self.x, self.y) if (z != z0).any(): msg = 'Max difference = %g' % abs((z - z0)/z0).max() result = False break self.assert_(result, msg) def test_repeat_2(self): "repeatability #2" z0 = calc(self.x, self.y) msg = '' result = True for i in xrange(self.nsim): x, y = load() z = calc(x, y) if (z != z0).any(): msg = 'Max difference = %g' % abs((z - z0)/z0).max() result = False break self.assert_(result, msg) def test_repeat_3(self): "repeatability #3" z0 = calc(100*self.x, self.y) / (100 * 100) msg = '' result = True for i in xrange(self.nsim): x, y = load() z = calc(100*x, y) / (100 * 100) if (z != z0).any(): msg = 'Max difference = %g' % abs((z - z0)/z0).max() result = False break self.assert_(result, msg) def testsuite(): unit = unittest.TestLoader().loadTestsFromTestCase s = [] s.append(unit(Test_repeat)) return unittest.TestSuite(s) def run(): suite = testsuite() unittest.TextTestRunner(verbosity=2).run(suite)
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