pygsti.tools.matrixtools.sign_fix_qr

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pygsti.tools.matrixtools.sign_fix_qr#

sign_fix_qr(q, r, tol=1e-06)#

Change the signs of the columns of Q and rows of R to follow a convention.

Flips the signs of Q-columns and R-rows from a QR decomposition so that the largest absolute element in each Q-column is positive. This is an arbitrary but consistent convention that resolves sign-ambiguity in the output of a QR decomposition.

Parameters:

  • q (numpy.ndarray) – Input Q and R matrices from QR decomposition.

  • r (numpy.ndarray) – Input Q and R matrices from QR decomposition.

  • tol (float, optional) – Tolerance for computing the maximum element, i.e., anything within tol of the true max is counted as a maximal element, the first of which is set positive by the convention.

Returns:

qq, rr – Updated versions of q and r.

Return type:

numpy.ndarray

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