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C
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C Parallel Sparse BLAS v2.0
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C (C) Copyright 2006 Salvatore Filippone University of Rome Tor Vergata
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C Alfredo Buttari University of Rome Tor Vergata
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C
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C Redistribution and use in source and binary forms, with or without
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C modification, are permitted provided that the following conditions
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C are met:
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C 1. Redistributions of source code must retain the above copyright
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C notice, this list of conditions and the following disclaimer.
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C 2. Redistributions in binary form must reproduce the above copyright
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C notice, this list of conditions, and the following disclaimer in the
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C documentation and/or other materials provided with the distribution.
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C 3. The name of the PSBLAS group or the names of its contributors may
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C not be used to endorse or promote products derived from this
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C software without specific written permission.
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C
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C THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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C ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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C TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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C PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE PSBLAS GROUP OR ITS CONTRIBUTORS
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C BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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C CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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C SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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C INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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C CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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C ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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C POSSIBILITY OF SUCH DAMAGE.
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C
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C
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***********************************************************************
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* *
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* REFERENCES = *
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* *
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* [1] D. E. Knuth *
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* The art of computer programming Vol. 1 *
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* Sect. 1.3.3 *
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* Addison-Wesley *
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* *
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* *
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* FUNCTION: Checks whether a vector really is a permutation *
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* works by exploiting the cycle structure of the *
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* permutation. *
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* *
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* *
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***********************************************************************
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LOGICAL FUNCTION ISAPERM(N,IP)
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implicit none
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C .. Scalar Arguments ..
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INTEGER N
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C ..
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C .. Array Arguments ..
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INTEGER IP(N)
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C ..
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C .. Local Scalars ..
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INTEGER I,J,M
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C ..
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ISAPERM = .TRUE.
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C
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C Sanity check first
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C
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DO I=1, N
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IF ((IP(I).LT.1).OR.(IP(I).GT.N)) THEN
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ISAPERM = .FALSE.
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RETURN
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ENDIF
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ENDDO
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C
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C Now work through the cycles, by marking each successive item as negative.
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C No cycle should intersect with any other, hence the .GE.1 check.
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C
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DO M = 1, N
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I = IP(M)
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IF (I.LT.0) THEN
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IP(M) = -I
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ELSE IF (I.NE.M) THEN
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J = IP(I)
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IP(I) = -J
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I = J
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DO WHILE ((J.GE.1).AND.(J.NE.M))
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J = IP(I)
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IP(I) = -J
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I = J
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ENDDO
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IP(M) = IABS(IP(M))
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IF (J.NE.M) THEN
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ISAPERM = .FALSE.
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DO I=1, N
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IP(I) = IABS(IP(I))
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ENDDO
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GOTO 9999
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ENDIF
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END IF
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ENDDO
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9999 CONTINUE
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RETURN
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END
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