The motivation here is be consistent in having n-qubit operators represented by 2n-bit strings in which the first (last) n bits indicate the support of X-type (Z-type) operators. In order to extract, say, syndrome = parity_check_matrix @ error for a n-qubit error operator, we therefore need the rows of the parity check matrix to look like [z_support|x_support].
(... yet again)
The motivation here is be consistent in having
n-qubit operators represented by2n-bit strings in which the first (last)nbits indicate the support of X-type (Z-type) operators. In order to extract, say,syndrome = parity_check_matrix @ errorfor an-qubit error operator, we therefore need the rows of the parity check matrix to look like[z_support|x_support].