The array descriptor **DESC_**
whose type is defined as
**DESC_(DTYPE_)=501** ,
is an integer array of length 7.
This descriptor type is used in
the ScaLAPACK narrow band routines
and tridiagonal routines to specify
a block-column distribution of a
global array over a one-dimensional
process grid. In the general and
symmetric positive definite banded
and tridiagonal routines, a
one-dimensional block-column
distribution is specified for
the coefficient matrix .
The matrix of right-hand-side
vectors must be distributed
over a one-dimensional process
grid using a block-row data
distribution. Refer to
section 4.4.1
for further details on block
data distribution.

Let us assume, for example,
that we have an array descriptor
*DESCA* for a block-column
distributed array *A*. For
readability of the code, we
have associated symbolic names
with the descriptor entries.
As previously mentioned, the
notations x_ used in the
entries of the array descriptor
denote the attributes of a
global array. For readability
of the code, we have associated
symbolic names for the descriptor
entries. For example, N_
denotes the number of columns
and N_A specifically denotes
the number of columns in global
array *A*.

**Table 4.11:** Content of the array descriptor for in-core narrow band
and tridiagonal coefficient matrices

When *A* is non-symmetric and
factorized without pivoting,
LLD_A must be at least
*BWL*+1+*BWU*. When *A* is
non-symmetric and factorized
with partial pivoting, LLD_A
must be at least 2(*BWL*+*BWU*)+1.
When *A* is symmetric positive
definite, LLD_A must be at least
*BW*+1. Finally, when *A* is
tridiagonal, LLD_A is not
referenced.

Tue May 13 09:21:01 EDT 1997