Restore approx 0 rounding to decomp0 method #4862
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In Qiskit#4656 we added rounding to the output of the decomp0 method to handle a case where differing FP precision on windows environments was causing an expected result in running two_qubit_cnot_decompose on np.eye(4) with numpy 1.19.x installed leading to a hard failure in the qasm tests. This seemed to reliably unblock testing and make unit tests work reliably. However, that original fix from Qiskit#4656 was superseded by Qiskit#4835 which was a fix for a more general issue with the reproducibility of the decompositions and reverted. Since Qiskit#4835 has merged we've been seeing an uptick in the failure rate on the same unitary qasm test that Qiskit#4656 fixed, so the change in Qiskit#4835 was not actually sufficient for the windows case. This commit restores the fix from Qiskit#4656 to unblock CI and fix the reproducability of the decompositions across systems. Fixes Qiskit#4856
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kdk
approved these changes
Aug 4, 2020
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Summary
In #4656 we added rounding to the output of the decomp0 method to handle
a case where differing FP precision on windows environments was causing
an expected result in running two_qubit_cnot_decompose on np.eye(4)
with numpy 1.19.x installed leading to a hard failure in the qasm tests.
This seemed to reliably unblock testing and make unit tests work
reliably. However, that original fix from #4656 was superseded by #4835
which was a fix for a more general issue with the reproducibility of the
decompositions and reverted. Since #4835 has merged we've been seeing an
uptick in the failure rate on the same unitary qasm test that #4656
fixed, so the change in #4835 was not actually sufficient for the
windows case. This commit restores the fix from #4656 to unblock CI and
fix the reproducability of the decompositions across systems.
Details and comments
Fixes #4856