You cannot select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
psblas3/base/serial/aux/isaperm.f

100 lines
4.5 KiB
Fortran

C
C Parallel Sparse BLAS v2.0
C (C) Copyright 2006 Salvatore Filippone University of Rome Tor Vergata
C Alfredo Buttari University of Rome Tor Vergata
C
C Redistribution and use in source and binary forms, with or without
C modification, are permitted provided that the following conditions
C are met:
C 1. Redistributions of source code must retain the above copyright
C notice, this list of conditions and the following disclaimer.
C 2. Redistributions in binary form must reproduce the above copyright
C notice, this list of conditions, and the following disclaimer in the
C documentation and/or other materials provided with the distribution.
C 3. The name of the PSBLAS group or the names of its contributors may
C not be used to endorse or promote products derived from this
C software without specific written permission.
C
C THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
C ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
C TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
C PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE PSBLAS GROUP OR ITS CONTRIBUTORS
C BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
C CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
C SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
C INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
C CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
C ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
C POSSIBILITY OF SUCH DAMAGE.
C
C
***********************************************************************
* *
* REFERENCES = *
* *
* [1] D. E. Knuth *
* The art of computer programming Vol. 1 *
* Sect. 1.3.3 *
* Addison-Wesley *
* *
* *
* FUNCTION: Checks whether a vector really is a permutation *
* works by exploiting the cycle structure of the *
* permutation. *
* *
* *
***********************************************************************
LOGICAL FUNCTION ISAPERM(N,IP)
C .. Scalar Arguments ..
INTEGER N
C ..
C .. Array Arguments ..
INTEGER IP(N)
C ..
C .. Local Scalars ..
INTEGER I,J,M
C ..
ISAPERM = .TRUE.
C
C Sanity check first
C
DO I=1, N
IF ((IP(I).LT.1).OR.(IP(I).GT.N)) THEN
ISAPERM = .FALSE.
RETURN
ENDIF
ENDDO
C
C Now work through the cycles, by marking each successive item as negative.
C No cycle should intersect with any other, hence the .GE.1 check.
C
DO M = 1, N
I = IP(M)
IF (I.LT.0) THEN
IP(M) = -I
ELSE IF (I.NE.M) THEN
J = IP(I)
IP(I) = -J
I = J
DO WHILE ((J.GE.1).AND.(J.NE.M))
J = IP(I)
IP(I) = -J
I = J
ENDDO
IP(M) = IABS(IP(M))
IF (J.NE.M) THEN
ISAPERM = .FALSE.
DO I=1, N
IP(I) = IABS(IP(I))
ENDDO
GOTO 9999
ENDIF
END IF
ENDDO
9999 CONTINUE
RETURN
END