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## Array Descriptor for Out-core Dense Matrices

The array descriptor DESC_ whose type is defined as DESC_(DTYPE_)=601 , is an integer array of length 11. DESC_(DTYPE_)=601 is used for the ScaLAPACK routines involved in the out-of-core solution of dense linear systems using LU, QR or Cholesky factorizations [55]. The matrix stored on disk is composed of records each record of which corresponds to an MMB NNB DESC_(DTYPE_)=1 ScaLAPACK matrix and these records are organized in a column major (Fortran array) manner. The array descriptor for out-of-core matrices has extra fields to store file parameters associated with the matrix, such as the I/O device unit number, MMB and NNB, and the amount of temporary buffer storage available.

Similar to DESC_(DTYPE_)=1 symmetric ScaLAPACK matrices, only the upper (UPLO='U') triangle or the lower (UPLO='L') triangle is accessed. The entire coefficient matrix is stored on disk, regardless of whether the matrix is nonsymmetric or symmetric.

Table 4.13: Content of the array descriptor for out-of-core dense matrices