Arguments

AP

(input/output) REAL or COMPLEX array, shape $(:)$ with $size(AP) = n(n+1)/2$, where $n$ is the order of $A$.
On entry, the upper or lower triangle of matrix $A$ in packed storage. The elements are stored columnwise as follows:

$$\begin{array}{c\vert c\vert c} A_{i,j} & i,j & {\bf UPLO} ... ... \leq i \leq n \end{array} & \mbox{ 'L'} \\ \hline \end{array}$$

On exit, the block diagonal matrix $D$ and the multipliers used to obtain $U$ or $L$ from the factorization of $A$, stored as a packed triangular matrix in the same storage format as $A$.

B

(input/output) REAL or COMPLEX array, shape $(:,:)$ with $size({\bf B},1) = n$ or shape $(:)$ with $size({\bf B}) = n$.
On entry, the matrix $B$.
On exit, the solution matrix $X$.

UPLO

Optional (input) CHARACTER(LEN=1)


Default value: 'U'.

IPIV

Optional (output) INTEGER array, shape $(:)$ with $size({\bf IPIV})=n$.
Details of the row and column interchanges and the block structure of $D$.
If ${\bf IPIV}_k > 0$, then rows and columns $k$ and ${\bf IPIV}_k$ were interchanged, and $D_{k,k}$ is a $1 \times 1$ diagonal block.
If ${\bf IPIV}_k < 0$, then there are two cases:

INFO

Optional (output) INTEGER.


If INFO is not present and an error occurs, then the program is terminated with an error message.

References: [1] and [17,9,20,21].