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@ -33,39 +33,39 @@ range(2, 22)
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* Naïve Sherman-Morrison
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:PROPERTIES:
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:Name: qmckl_sherman_morrison_naive
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:CRetType: qmckl_exit_code
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:FRetType: qmckl_exit_code
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:END:
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:PROPERTIES:
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:Name: qmckl_sherman_morrison_naive
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:CRetType: qmckl_exit_code
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:FRetType: qmckl_exit_code
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:END:
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This is the simplest of the available Sherman-Morrison-Woodbury kernels. It applies rank-1 updates one by one in
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the order that is given. It only checks if the denominator in the Sherman-Morrison formula is not too close to
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zero when an update is evaluated. It will exit with an error code of the denominator is too close to zero.
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This is the simplest of the available Sherman-Morrison-Woodbury kernels. It applies rank-1 updates one by one in
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the order that is given. It only checks if the denominator in the Sherman-Morrison formula is not too close to
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zero when an update is evaluated. It will exit with an error code of the denominator is too close to zero.
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The formula for any update $u_j$ (index $j$ is suppresed for clarity) that is applied is
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\[
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(S + uv^T)^{-1} = S^{-1} - \frac{S^{-1} uv^T S^{-1}}{1 + v^T S^{-1} u}
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\]
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The formula for any update $u_j$ (index $j$ is suppresed for clarity) that is applied is
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\[
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(S + uv^T)^{-1} = S^{-1} - \frac{S^{-1} uv^T S^{-1}}{1 + v^T S^{-1} u}
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\]
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where
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$S$ is the Slater-matrix,
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$u$ and $v^T$ are the column and row vectors containing the updates,
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$S^{-1}$ is the inverse of the Slater-matrix.
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where
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$S$ is the Slater-matrix,
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$u$ and $v^T$ are the column and row vectors containing the updates,
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$S^{-1}$ is the inverse of the Slater-matrix.
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Even though the Slater-matrix $S$ with all updates applied at once is invertable, during the course of applying
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updates to the inverse Slater-matrix $S^{-1}$ one-by-one it can happen that one of the intermediate inverse
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matrices $S^{-1}$ becomes singular. Therefore a global threshold value $\epsilon$ is defined that is used to
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evaluate each individual update $u_j$ when it is applied.
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Even though the Slater-matrix $S$ with all updates applied at once is invertable, during the course of applying
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updates to the inverse Slater-matrix $S^{-1}$ one-by-one it can happen that one of the intermediate inverse
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matrices $S^{-1}$ becomes singular. Therefore a global threshold value $\epsilon$ is defined that is used to
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evaluate each individual update $u_j$ when it is applied.
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This value sets the lower bound for which the
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denominator $1+v_j^TS^{-1}u_j$ is considered to be too small and will most probably result in a singular matrix
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$S$, or at least in an inverse of $S$ of very poor numerical quality. Therefore, when $1+v_j^TS^{-1}u_j \geq \epsilon$,
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the update is applied as usual and the kernel exits with return code \texttt{QMCKL_SUCCESS}.
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If $1+v_j^TS^{-1}u_j \leq \epsilon$ the update is rejected and the kernel exits with return code \texttt{QMCKL_FAILURE}.
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This value sets the lower bound for which the
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denominator $1+v_j^TS^{-1}u_j$ is considered to be too small and will most probably result in a singular matrix
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$S$, or at least in an inverse of $S$ of very poor numerical quality. Therefore, when $1+v_j^TS^{-1}u_j \geq \epsilon$,
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the update is applied as usual and the kernel exits with return code \texttt{QMCKL_SUCCESS}.
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If $1+v_j^TS^{-1}u_j \leq \epsilon$ the update is rejected and the kernel exits with return code \texttt{QMCKL_FAILURE}.
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If the determinant of the Slater-matrix is passed, it will be updated to the determinant resulting
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from applying the updates to the original matrix.
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If the determinant of the Slater-matrix is passed, it will be updated to the determinant resulting
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from applying the updates to the original matrix.
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#+NAME: qmckl_sherman_morrison_naive_args
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| Variable | Type | In/Out | Description |
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@ -612,9 +612,9 @@ end interface
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* End of files
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#+begin_src c :comments link :tangle (eval c_test)
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assert (qmckl_context_destroy(context) == QMCKL_SUCCESS);
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return 0;
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#+begin_src c :comments link :tangle (eval c_test)
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assert (qmckl_context_destroy(context) == QMCKL_SUCCESS);
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return 0;
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}
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#+end_src
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