Contents

p?trmr2d

Copies a submatrix from one trapezoidal matrix to another.

Syntax

Include Files
• mkl_scalapack.h
Description
The
p?trmr2d
function
copies the indicated matrix or submatrix of
A
to the indicated matrix or submatrix of
B
. It provides a truly general copy from any block cyclicly-distributed matrix or submatrix to any other block cyclicly-distributed matrix or submatrix. With
p?gemr2d
, these
functions
are the only ones in the ScaLAPACK library which provide inter-context operations: they can take a matrix or submatrix
A
in context
A
(distributed over process grid
A
) and copy it to a matrix or submatrix
B
in context
B
(distributed over process grid
B
).
The
p?trmr2d
function
assumes the matrix or submatrix to be trapezoidal. Only the upper or lower part is copied, and the other part is unchanged.
There does not need to be a relationship between the two operand matrices or submatrices other than their global size and the fact that they are both legal block cyclicly-distributed matrices or submatrices. This means that they can, for example, be distributed across different process grids, have varying block sizes and differing matrix starting points, or be contained in different sized distributed matrices.
Take care when context
A
is disjoint from context
B
. The general rules for which parameters need to be set are:
• All calling processes must have the correct
m
and
n
.
• Processes in context
A
must correctly define all parameters describing
A
.
• Processes in context
B
must correctly define all parameters describing
B
.
• Processes which are not members of context
A
must pass
ctxt_a
= -1 and need not set other parameters describing
A
.
• Processes which are not members of context
B
must pass
ctxt_b
= -1 and need not set other parameters describing
B
.
Because of its generality,
p?trmr2d
can be used for many operations not usually associated with copy
functions
. For instance, it can be used to a take a matrix on one process and distribute it across a process grid, or the reverse. If a supercomputer is grouped into a virtual parallel machine with a workstation, for instance, this
function
can be used to move the matrix from the workstation to the supercomputer and back. In ScaLAPACK, it is called to copy matrices from a two-dimensional process grid to a one-dimensional process grid. It can be used to redistribute matrices so that distributions providing maximal performance can be used by various component libraries, as well.
Note that this
function
requires an array descriptor with
dtype_
= 1.
Product and Performance Information
Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.
Notice revision #20201201
Input Parameters
uplo
(global) Specifies whether to copy the upper or lower part of the matrix or submatrix.
uplo
=
'U'
Copy the upper triangular part.
uplo
=
'L'
Copy the lower triangular part.
diag
(global) Specifies whether to copy the diagonal of the matrix or submatrix.
diag
=
'U'
Do not copy the diagonal.
diag
=
'N'
Copy the diagonal.
m
(global) The number of rows of matrix
A
to be copied (
m
0).
n
(global) The number of columns of matrix
A
to be copied (
n
0).
a
(local)
Pointer into the local memory to array of size
lld_a
*
LOCc
(
ja
+
n
-1)
containing the source matrix
A
.
ia
,
ja
(global) The row and column indices in the array
A
indicating the first row and the first column, respectively, of the submatrix of
A
) to copy. 1
ia
total_rows_in_a
-
m
+1, 1
ja
total_columns_in_a
-
n
+1.
desca
(global and local) array of size
dlen_
. The array descriptor for the distributed matrix
A
.
Only
dtype_a
= 1 is supported, so
dlen_
= 9.
If the calling process is not part of the context of
A
,
ctxt_a
must be equal to -1.
ib
,
jb
(global) The row and column indices in the array
B
indicating the first row and the first column, respectively, of the submatrix
B
to which to copy the matrix. 1
ib
total_rows_in_b
-
m
+1, 1
jb
total_columns_in_b
-
n
+1.
descb
(global and local) array of size
dlen_
. The array descriptor for the distributed matrix
B
.
Only
dtype_b
= 1 is supported, so
dlen_
= 9.
If the calling process is not part of the context of
B
,
ctxt_b
must be equal to -1.
ictxt
(global).
The context encompassing at least the union of all processes in context
A
and context
B
. All processes in the context
ictxt
must call this
function
, even if they do not own a piece of either matrix.
Output Parameters
b
Pointer into the local memory to array of size
lld_b
*
LOCc
(
jb+n-1
)
.
Overwritten by the submatrix from
A
.

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.