## MA02OD

### Compute the number of zero rows (and zero columns) of a real (skew-)Hamiltonian matrix

[Specification] [Arguments] [Method] [References] [Comments] [Example]

Purpose

```  To compute the number of zero rows (and zero columns) of a real
(skew-)Hamiltonian matrix,

(  A    D   )
H = (           ).
(  E  +/-A' )

```
Specification
```      INTEGER FUNCTION MA02OD( SKEW, M, A, LDA, DE, LDDE )
C     .. Scalar Arguments ..
CHARACTER          SKEW
INTEGER            LDA, LDDE, M
C     .. Array Arguments ..
DOUBLE PRECISION   A( LDA, * ), DE( LDDE, * )

```
Function Value
```  MA02OD  INTEGER
The number of zero rows.

```
Arguments

Mode Parameters

```  SKEW    CHARACTER*1
Specifies whether the matrix is Hamiltonian or skew-
Hamiltonian as follows:
= 'H':  The matrix is Hamiltonian;
= 'S':  The matrix is skew-Hamiltonian.

```
Input/Output Parameters
```  M       (input) INTEGER
The order of the matrices A, D, and E.  M >= 0.

A       (input) DOUBLE PRECISION array, dimension (LDA,M)
The leading M-by-M part of this array must contain the
matrix A.

LDA     INTEGER
The leading dimension of the array A.  LDA >= max(1,M).

DE      (input) DOUBLE PRECISION array, dimension (LDDE,M+1)
The leading M-by-M lower triangular part of this array
must contain the lower triangular part of the (skew-)
symmetric matrix E, and the M-by-M upper triangular
part of the submatrix in the columns 2 to M+1 of this
array must contain the upper triangular part of the
(skew-)symmetric matrix D. If S is skew-Hamiltonian, the
parts containing the diagonal and the first superdiagonal
of this array, which should be zero, are not referenced.

LDDE    INTEGER
The leading dimension of the array DE.  LDDE >= MAX(1,M).

```
```  None
```
Example

Program Text

```  None
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Program Data
```  None
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Program Results
```  None
```