Tweak DM normalization after factor #5922
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daxfohl
commented
Oct 17, 2022
daxfohl
commented
Oct 31, 2022
| @@ -717,6 +717,11 @@ def factor_density_matrix( | |||
| t2 = transpose_density_matrix_to_axis_order(t1, product_axes) | |||
| if not np.allclose(t2, t, atol=atol): | |||
| raise ValueError('The tensor cannot be factored by the requested axes') | |||
| # Tweak trace back to 1 to avoid rounding error propagation | |||
| extracted_dim = int(np.sqrt(np.prod(extracted.shape))) | |||
| extracted /= np.trace(extracted.reshape((extracted_dim, extracted_dim))) | |||
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Open question: should this go into partial_trace instead? Since it appears that partial_trace is the root cause of the rounding error.
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I'm closing this because I think the right thing to do here is to do this in Of course fixing this in |
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As reported in #5916, when repeatedly factoring and kronning a density matrix during simulation, the rounding error caused by partial_trace can propagate and explode after about 15 repetitions. This PR explicitly re-normalizes the density matrix after factoring.
Fixes #5916