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allen-tildesley-book
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README,
f.00,
f.01,
f.02,
f.03,
f.04,
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f.06,
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f.09,
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f.31,
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f.33,
f.34,
f.35,
f.36,
f.37,
older-version
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********************************************************************************
** FICHE F.34. AN EFFICIENT CLUSTERING ROUTINE **
** This FORTRAN code is intended to illustrate points made in the text. **
** To our knowledge it works correctly. However it is the responsibility of **
** the user to test it, if it is to be used in a research application. **
********************************************************************************
SUBROUTINE MYGANG ( RCL, IT, NIT )
COMMON / BLOCK1 / RX, RY, RZ
C *******************************************************************
C ** ROUTINE TO IDENTIFY ATOM CLUSTERS IN A CONFIGURATION. **
C ** **
C ** THIS ROUTINE SORTS N ATOMS INTO CLUSTERS DEFINED BY A **
C ** CRITICAL CLUSTER RADIUS, AND COUNTS THE NUMBER OF ATOMS IN **
C ** THE CLUSTER CONTAINING THE ATOM 'IT'. THE ATOMS ARE IN A **
C ** BOX OF UNIT LENGTH CENTRED AT THE ORIGIN **
C ** **
C ** REFERENCE: **
C ** **
C ** STODDARD J COMP PHYS, 27, 291, 1977. **
C ** **
C ** PRINCIPAL VARIABLES: **
C ** **
C ** INTEGER N NUMBER OF ATOMS **
C ** INTEGER IT AN ATOM IN A PARTICULAR CLUSTER **
C ** INTEGER L(N) A LINKED-LIST **
C ** INTEGER NIT NUMBER OF ATOMS IN THAT CLUSTER **
C ** REAL RX(N),RY(N),RZ(N) POSITIONS **
C ** REAL RCL CRITICAL CLUSTER DISTANCE **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
REAL RX(N), RY(N), RZ(N)
REAL RCL
INTEGER IT, NIT
REAL RCLSQ, RXJK, RYJK, RZJK
REAL RJKSQ, RXJ, RYJ, RZJ
INTEGER I, J, K, LK, LIT, L(N)
C ****************************************************************
RCLSQ = RCL * RCL
C ** SET UP THE SORTING ARRAY **
DO 10 I = 1, N
L(I) = I
10 CONTINUE
C ** SORT THE CLUSTERS **
DO 50 I = 1, N - 1
IF ( I .EQ. L(I) ) THEN
J = I
RXJ = RX(J)
RYJ = RY(J)
RZJ = RZ(J)
DO 20 K = I + 1, N
LK = L(K)
IF ( LK .EQ. K ) THEN
RXJK = RXJ - RX(K)
RYJK = RYJ - RY(K)
RZJK = RZJ - RZ(K)
RXJK = RXJK - ANINT ( RXJK )
RYJK = RYJK - ANINT ( RYJK )
RZJK = RZJK - ANINT ( RZJK )
RJKSQ = RXJK * RXJK + RYJK * RYJK + RZJK * RZJK
IF ( RJKSQ .LE. RCLSQ ) THEN
L(K) = L(J)
L(J) = LK
ENDIF
ENDIF
20 CONTINUE
J = L(J)
RXJ = RX(J)
RYJ = RY(J)
RZJ = RZ(J)
30 IF ( J .NE. I ) THEN
DO 40 K = I + 1, N
LK = L(K)
IF ( LK .EQ. K ) THEN
RXJK = RXJ - RX(K)
RYJK = RYJ - RY(K)
RZJK = RZJ - RZ(K)
RXJK = RXJK - ANINT ( RXJK )
RYJK = RYJK - ANINT ( RYJK )
RZJK = RZJK - ANINT ( RZJK )
RJKSQ = RXJK * RXJK + RYJK * RYJK + RZJK * RZJK
IF ( RJKSQ .LE. RCLSQ ) THEN
L(K) = L(J)
L(J) = LK
ENDIF
ENDIF
40 CONTINUE
J = L(J)
RXJ = RX(J)
RYJ = RY(J)
RZJ = RZ(J)
GO TO 30
ENDIF
ENDIF
50 CONTINUE
C ** COUNT THE NUMBER IN A CLUSTER CONTAINING ATOM IT **
NIT = 1
LIT = L(IT)
60 IF ( LIT .NE. IT ) THEN
NIT = NIT + 1
LIT = L(LIT)
GO TO 60
ENDIF
RETURN
END
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