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# Array Descriptors

An array descriptor is associated with each global array. This array stores the information required to establish the mapping between each global array entry and its corresponding process and memory location. The notations x_ used in the entries of the array descriptor denote the attributes of a global array. For example, M_ denotes the number of rows and M_A specifically denotes the number of rows in global matrix A. These descriptors assume different storage for the global data. The length of the array descriptor is specified by DLEN_ and varies according to the descriptor type DTYPE_.

Array descriptors are provided for

- dense matrices,
- band and tridiagonal matrices, and
- out-of-core matrices

and are differentiated by the DTYPE_ entry in the descriptor. At the present time the following values of DESC_(DTYPE_) are valid.

Table 4.2: Valid values of DESC_(DTYPE_)