On entry: the
$n$ by
$n$ symmetric indefinite matrix
$A$.
If ${\mathbf{order}}=\mathrm{Nag\_ColMajor}$, ${A}_{ij}$ is stored in ${\mathbf{a}}\left[\left(j-1\right)\times {\mathbf{pda}}+i-1\right]$.
If ${\mathbf{order}}=\mathrm{Nag\_RowMajor}$, ${A}_{ij}$ is stored in ${\mathbf{a}}\left[\left(i-1\right)\times {\mathbf{pda}}+j-1\right]$.
If ${\mathbf{uplo}}=\mathrm{Nag\_Upper}$, the upper triangular part of $A$ must be stored and the elements of the array below the diagonal are not referenced.
If ${\mathbf{uplo}}=\mathrm{Nag\_Lower}$, the lower triangular part of $A$ must be stored and the elements of the array above the diagonal are not referenced.
On exit: the upper or lower triangle of
$A$ is overwritten by details of the block diagonal matrix
$D$ and the multipliers used to obtain the factor
$U$ or
$L$ as specified by
uplo.