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Recursive cholesky #710

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EdDAzevedo
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Implement recursive formulation of Cholesky factorization for n by n symmetric positive definite matrix A.

Let the following be a block partitioning of matrix A.

Here submatrix L22 is n/2 by n/2, L11 is n1 by n1, where n1 = n - n/2, or partition matrix at mid-point

[L11 0 ] * [ L11' L21'] = [A11 A21' ]
[L21 L22] [ L22'] [A21 A22 ]

(1) L11 * L11' = A11 , recursive Cholesky factorization

(2) L21 * L11' = A21 or
L21 = A21 / L11' triangular solve (TRSM)

(3) L21 * L21' + L22 * L22' = A22
or
(3a) A22 <- A22 - L21 * L21', symmetric rank-k update (SYRK)
(3b) L22 * L22' = A22, recursive Cholesky factorization

Note C++ recursion is performed on CPU host and the recursion depth is O( log2( n ) ).

@tfalders tfalders added the noOptimizations Disable optimized kernels for small sizes for some routines label May 27, 2024
@tfalders
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I have opened a PR on your local fork with my suggested changes. Please have a look when you have a chance.

* Cleanup for recursive Cholesky

* Added ROCBLAS_CHECK to all nested calls in potrf

* Removed unused variables

* Add back offset variables

* Reintroduce row_offset

* Added row_offset to the log
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