Web pdp-10.trailing-edge.com

Trailing-Edge - PDP-10 Archives - decuslib10-02 - 43,50145/perm.doc
There are 2 other files named perm.doc in the archive. Click here to see a list.
```SUBROUTINE PERM

PURPOSE
TO COMPUTE THE PERMUTATION VECTOR THAT IS INVERSE TO A GIVEN
PERMUTATION VECTOR, THE PERMUTATION VECTOR THAT IS EQUIVA-
LENT TO A GIVEN TRANSPOSITION VECTOR AND A TRANSPOSITION
VECTOR THAT IS EQUIVALENT TO A GIVEN PERMUTATION VECTOR.
(SEE THE GENERAL DISCUSSION FOR DEFINITIONS AND NOTATION.)

USAGE
CALL PERM(IP1,IP2,N,IPAR,IER)

DESCRIPTION OF PARAMETERS
IP1	- GIVEN PERMUTATION OR TRANSPOSITION VECTOR
(DIMENSION N)
IP2	- RESULTING PERMUTATION OR TRANSPOSITION VECTOR
(DIMENSION N)
N	- DIMENSION OF VECTORS IP1 AND IP2
IPAR - INPUT PARAMETER
IPAR NEGATIVE - COMPUTE THE PERMUTATION VECTOR IP2
THAT IS THE INVERSE OF THE PERMUTA-
TION VECTOR IP1
IPAR	=  ZERO - COMPUTE THE PERMUTATION VECTOR IP2
THAT IS EQUIVALENT TO THE TRANSPOSI-
TION VECTOR IP1
IPAR POSITIVE - COMPUTE A TRANSPOSITION VECTOR IP2
THAT IS EQUIVALENT TO THE PERMUTATION
VECTOR IP1
IER	- RESULTING ERROR PARAMETER
IER=-1  -  N IS NOT POSITIVE
IER= 0  -  NO ERROR
IER= 1  -  IP1 IS EITHER NOT A PERMUTATION VECTOR OR
NOT A TRANSPOSITION VECTOR ON 1,...,N,
DEPENDING ON WHETHER IPAR IS NON-ZERO OR
ZERO, RESPECTIVELY

REMARKS
(1)	IF IER=-1 THERE HAS BEEN NO COMPUTATION.
(2)	IF IER=1, THEN COMPUTATION HAS BEEN UNSUCCESSFUL DUE TO
ERROR AND THE PARTIAL RESULTS FOUND IN IP2 ARE USELESS.
(3)	IP2 CANNOT HAVE THE SAME STORAGE ALLOCATION AS IP1.

SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
NONE

METHOD
(1)	IPAR NEGATIVE - FOR EACH I, I=1,...,N, IP2(IP1(I)) IS
SET TO I.
(2)	IPAR  =  ZERO - INITIALLY IP2(I) IS SET TO I FOR
I=1,...,N.  THEN, FOR I=1,...,N IN THAT
ORDER, IP2(I) AND IP2(IP1(I)) ARE
INTERCHANGED.
(3)	IPAR POSITIVE - INITIALLY IP1 IS MOVED TO IP2.	THEN
THE FOLLOWING TWO STEPS ARE REPEATED
FOR I SUCCESSIVELY EQUAL TO 1,...,N.
(A) FIND THE SMALLEST J GREATER THAN OR
EQUAL TO I SUCH THAT IP2(J)=I.
(B) SET IP2(J) TO IP2(I).
```