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md-nvt-extended.f
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md-nvt-extended.f
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********************************************************************************
** FICHE F.28. CONSTANT-NVT MOLECULAR DYNAMICS - EXTENDED SYSTEM METHOD **
** 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. **
********************************************************************************
PROGRAM NOSE
COMMON / BLOCK1 / RX, RY, RZ, VX, VY, VZ, AX, AY, AZ,
: BX, BY, BZ, CX, CY, CZ, FX, FY, FZ
COMMON / BLOCK2 / S, SV, SA, SB, SC, SF
C *******************************************************************
C ** CONSTANT-NVT MOLECULAR DYNAMICS USING AN EXTENDED SYSTEM. **
C ** **
C ** REFERENCE: **
C ** **
C ** NOSE, MOLEC. PHYS. 52, 255, 1984. **
C ** **
C ** ROUTINES REFERENCED: **
C ** **
C ** SUBROUTINE FORCE ( BOX, RCUT, V, VC, W ) **
C ** CALCULATES ACCELERATIONS, POTENTIAL AND VIRIAL **
C ** SUBROUTINE KINET ( K ) **
C ** CALCULATES KINETIC ENERGY **
C ** SUBROUTINE READCN ( CNFILE, BOX ) **
C ** READS CONFIGURATION **
C ** SUBROUTINE WRITCN ( CNFILE, BOX ) **
C ** WRITES CONFIGURATION **
C ** SUBROUTINE PREDIC ( DT ) **
C ** PREDICTS POSITIONS AT TIME T + DT **
C ** SUBROUTINE CORREC ( DT ) **
C ** CORRECTS POSITIONS AT TIME T + DT **
C ** **
C ** PRINCIPAL VARIABLES: **
C ** **
C ** INTEGER N NUMBER OF ATOMS **
C ** REAL DT TIMESTEP **
C ** REAL RX(N),RY(N),RZ(N) ATOM POSITIONS **
C ** REAL VX(N),VY(N),VZ(N) FIRST DERIVATIVES **
C ** REAL AX(N),AY(N),AZ(N) SECOND DERIVATIVES **
C ** REAL BX(N),BY(N),BZ(N) THIRD DERIVATIVES **
C ** REAL FX(N),FY(N),FZ(N) TOTAL FORCES **
C ** REAL S,SV,SA,SB,SC,SF S AND DERIVATIVES **
C ** REAL Q THERMAL INERTIA **
C ** REAL ACV,ACK ETC. AV VALUE ACCUMULATORS **
C ** REAL AVV,AVK ETC. AV VALUES **
C ** REAL ACVSQ, ACKSQ ETC. AV**2 VAL ACCUMULATORS **
C ** REAL FLV, FLK ETC. FLUCT AVERAGES **
C ** **
C ** USAGE: **
C ** **
C ** THE MODIFIED EQUATIONS OF MOTION ARE AS FOLLOWS: **
C ** A = F/(M*S**2) - 2*SV*V/S **
C ** SA = (SUM (M*S/Q)*V**2 ) - ((3N-3)+1)*KT/(Q*S) **
C ** WHERE R,V,A,.. ARE SUCCESSIVE DERIVATIVES OF POSITION **
C ** AND SV,SA,.... ARE SUCCESSIVE DERIVATIVES OF EXTRA VARIABLE S **
C ** F REPRESENTS FORCES, M PARTICLE MASS, Q EXTRA VARIABLE MASS **
C ** KT IS TEMPERATURE*BOLTZMANN'S CONSTANT **
C ** AND WE HAVE (3N-3) DEGREES OF FREEDOM IF MOMENTUM FIXED. **
C ** IN A SENSE, S IS A TIME-SCALING FACTOR. **
C ** WE SOLVE THESE EQUATIONS BY A GEAR 5-VALUE METHOD FOR SECOND **
C ** ORDER DIFFERENTIAL EQUATIONS. **
C ** THIS PROGRAM USES UNIT 10 FOR CONFIGURATION INPUT AND OUTPUT **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
REAL RX(N), RY(N), RZ(N), VX(N), VY(N), VZ(N)
REAL AX(N), AY(N), AZ(N), BX(N), BY(N), BZ(N)
REAL CX(N), CY(N), CZ(N), FX(N), FY(N), FZ(N)
REAL S, SV, SA, SB, SC, SF
INTEGER STEP, NSTEP, IPRINT
REAL Q, QK, QV
REAL ACV, ACK, ACE, ACEC, ACP, ACT, ACH, ACS
REAL AVV, AVK, AVE, AVEC, AVP, AVT, AVH, AVS
REAL ACVSQ, ACKSQ, ACESQ, ACECSQ, ACPSQ, ACTSQ
REAL ACHSQ, ACSSQ
REAL FLV, FLK, FLE, FLEC, FLP, FLT, FLH, FLS
REAL DT, DENS, TEMPER, RCUT, BOX, PRES, NORM, TEMP
REAL K, V, VC, W, E, EC, FREE, FREEN, H, VOL
REAL KN, VN, EN, ECN, HN
REAL SR3, SR9, VLRC, WLRC, PI
CHARACTER TITLE*80, CNFILE*30
PARAMETER ( PI = 3.1415927 )
PARAMETER ( FREE = 3.0 )
C *******************************************************************
C ** READ IN INITIAL PARAMETERS **
WRITE(*,'(1H1,'' **** PROGRAM NOSE **** '')')
WRITE(*,'(//1X,''MOLECULAR DYNAMICS OF LENNARD-JONES ATOMS '')')
WRITE(*,'('' CONSTANT-NVT DYNAMICS BY THE METHOD OF NOSE '')')
WRITE(*,'('' ENTER RUN TITLE '')')
READ (*,'(A)') TITLE
WRITE(*,'('' ENTER NUMBER OF STEPS '')')
READ (*,*) NSTEP
WRITE(*,'('' ENTER INTERVAL BETWEEN PRINTS '')')
READ (*,*) IPRINT
WRITE(*,'('' ENTER CONFIGURATION FILENAME '')')
READ (*,'(A)') CNFILE
WRITE(*,'('' ENTER THE FOLLOWING IN L-J REDUCED UNITS '')')
WRITE(*,'('' ENTER TIMESTEP '')')
READ (*,*) DT
WRITE(*,'('' ENTER TEMPERATURE '')')
READ (*,*) TEMPER
WRITE(*,'('' ENTER POTENTIAL CUTOFF '')')
READ (*,*) RCUT
WRITE(*,'('' ENTER THERMAL INERTIA PARAMETER '')')
READ (*,*) Q
WRITE(*,'(//1X,A)') TITLE
WRITE(*,'('' NUMBER OF ATOMS = '',I6 )') N
WRITE(*,'('' NUMBER OF STEPS = '',I6 )') NSTEP
WRITE(*,'('' PRINT INTERVAL = '',I6 )') IPRINT
WRITE(*,'('' CONFIGURATION FILENAME '',A)') CNFILE
WRITE(*,'('' TIMESTEP = '',F10.5)') DT
WRITE(*,'('' TEMPERATURE = '',F10.5)') TEMPER
WRITE(*,'('' POTENTIAL CUTOFF = '',F10.5)') RCUT
WRITE(*,'('' THERMAL INERTIA = '',F10.2)') Q
FREEN = FREE * REAL ( N )
C ** READCN MUST READ IN INITIAL CONFIGURATION **
C ** AND ASSIGN VALUES TO S AND ITS DERIVATIVES **
CALL READCN ( CNFILE, BOX )
VOL = BOX ** 3
DENS = REAL ( N ) / VOL
WRITE(*,'('' DENSITY = '',F10.5)') DENS
C ** CALCULATE LONG-RANGE CORRECTIONS **
C ** NB: SPECIFIC TO LENNARD-JONES **
SR3 = ( 1.0 / RCUT ) ** 3
SR9 = SR3 ** 3
VLRC = ( 8.0 / 9.0 ) * PI * DENS * REAL ( N ) *
: ( SR9 - 3.0 * SR3 )
WLRC = ( 16.0 / 9.0 ) * PI * DENS * REAL ( N ) *
: ( 2.0 * SR9 - 3.0 * SR3 )
C ** ZERO ACCUMULATORS **
ACV = 0.0
ACK = 0.0
ACE = 0.0
ACEC = 0.0
ACP = 0.0
ACT = 0.0
ACH = 0.0
ACS = 0.0
ACVSQ = 0.0
ACKSQ = 0.0
ACESQ = 0.0
ACECSQ = 0.0
ACPSQ = 0.0
ACTSQ = 0.0
ACHSQ = 0.0
ACSSQ = 0.0
FLV = 0.0
FLK = 0.0
FLE = 0.0
FLEC = 0.0
FLP = 0.0
FLT = 0.0
FLH = 0.0
FLS = 0.0
IF ( IPRINT .LE. 0 ) IPRINT = NSTEP + 1
WRITE(*,'(//1X,''**** START OF DYNAMICS ****'')')
WRITE(*,10001)
C *******************************************************************
C ** MAIN LOOP BEGINS **
C *******************************************************************
DO 1000 STEP = 1, NSTEP
C ** IMPLEMENT ALGORITHM **
CALL PREDIC ( DT )
CALL FORCE ( BOX, RCUT, V, VC, W )
CALL KINET ( K )
SF = ( 2.0 * K - ( FREEN + 1.0 ) * TEMPER ) / ( S * Q )
CALL CORREC ( DT )
QK = 0.5 * Q * ( SV ** 2 )
QV = ( FREEN + 1.0 ) * TEMPER * LOG ( S )
V = V + VLRC
W = W + WLRC
E = K + V
EC = K + VC
H = K + VC + QK + QV
EN = E / REAL ( N )
VN = V / REAL ( N )
ECN = EC / REAL ( N )
HN = H / REAL ( N )
TEMP = KN * 2.0 / FREE
PRES = DENS * TEMP + W / VOL
C ** INCREMENT ACCUMULATORS **
ACE = ACE + EN
ACEC = ACEC + ECN
ACK = ACK + KN
ACV = ACV + VN
ACP = ACP + PRES
ACH = ACH + HN
ACS = ACS + S
ACESQ = ACESQ + EN ** 2
ACECSQ = ACECSQ + ECN ** 2
ACKSQ = ACKSQ + KN ** 2
ACVSQ = ACVSQ + VN ** 2
ACPSQ = ACPSQ + PRES ** 2
ACHSQ = ACHSQ + HN ** 2
ACSSQ = ACSSQ + S ** 2
C ** OPTIONALLY PRINT INFORMATION **
IF ( MOD ( STEP, IPRINT ) .EQ. 0 ) THEN
WRITE(*,'(1X,I8,8(2X,F10.4))')
: STEP, HN, EN, ECN, KN, VN, TEMP, PRES, S
ENDIF
1000 CONTINUE
C *******************************************************************
C ** MAIN LOOP ENDS **
C *******************************************************************
WRITE(*,'(/1X,''**** END OF DYNAMICS **** ''//)')
C ** WRITE OUT FINAL AVERAGES **
NORM = REAL ( NSTEP )
AVE = ACE / NORM
AVEC = ACEC / NORM
AVK = ACK / NORM
AVV = ACV / NORM
AVP = ACP / NORM
AVH = ACH / NORM
AVS = ACS / NORM
ACESQ = ( ACESQ / NORM ) - AVE ** 2
ACECSQ = ( ACECSQ / NORM ) - AVEC ** 2
ACKSQ = ( ACKSQ / NORM ) - AVK ** 2
ACVSQ = ( ACVSQ / NORM ) - AVV ** 2
ACPSQ = ( ACPSQ / NORM ) - AVP ** 2
ACHSQ = ( ACHSQ / NORM ) - AVH ** 2
ACSSQ = ( ACSSQ / NORM ) - AVS ** 2
IF ( ACESQ .GT. 0.0 ) FLE = SQRT ( ACESQ )
IF ( ACECSQ .GT. 0.0 ) FLEC = SQRT ( ACECSQ )
IF ( ACKSQ .GT. 0.0 ) FLK = SQRT ( ACKSQ )
IF ( ACVSQ .GT. 0.0 ) FLV = SQRT ( ACVSQ )
IF ( ACPSQ .GT. 0.0 ) FLP = SQRT ( ACPSQ )
IF ( ACHSQ .GT. 0.0 ) FLH = SQRT ( ACHSQ )
IF ( ACSSQ .GT. 0.0 ) FLS = SQRT ( ACSSQ )
AVT = AVK * 2.0 / FREE
FLT = FLK * 2.0 / FREE
WRITE(*,'('' AVERAGES'',8(2X,F10.5))')
: AVH, AVE, AVEC, AVK, AVV, AVT, AVP, AVS
WRITE(*,'('' FLUCTS '',8(2X,F10.5))')
: FLH, FLE, FLEC, FLK, FLV, FLT, FLP, FLS
C ** WRITE OUT FINAL CONFIGURATION **
CALL WRITCN ( CNFILE, BOX )
STOP
10001 FORMAT(//1X,'TIMESTEP ...HAMIL.. ..ENERGY..',
: ' CUTENERGY. ..KINETIC. ..POTENT..',
: ' ..TEMPER.. .PRESSURE. ....S.....'/)
END
SUBROUTINE FORCE ( BOX, RCUT, V, VC, W )
COMMON / BLOCK1 / RX, RY, RZ, VX, VY, VZ, AX, AY, AZ,
: BX, BY, BZ, CX, CY, CZ, FX, FY, FZ
C *******************************************************************
C ** LENNARD-JONES FORCE ROUTINE IN REDUCED UNITS **
C ** **
C ** THE POTENTIAL IS V(R) = 4*((1/R)**12-(1/R)**6) **
C ** WE INCLUDE SPHERICAL CUTOFF AND MINIMUM IMAGING IN CUBIC BOX. **
C ** TWO POTENTIAL ENERGIES ARE RETURNED. **
C ** V IS CALCULATED USING THE UNSHIFTED POTENTIAL. WHEN LONG- **
C ** RANGE TAIL CORRECTIONS ARE ADDED, THIS MAY BE USED TO **
C ** CALCULATE THERMODYNAMIC INTERNAL ENERGY ETC. **
C ** VC IS CALCULATED USING THE SHIFTED POTENTIAL WITH NO **
C ** DISCONTINUITY AT THE CUTOFF. THIS MAY BE USED TO CHECK THE **
C ** CONSERVATION LAWS. **
C ** **
C ** PRINCIPAL VARIABLES: **
C ** **
C ** INTEGER N NUMBER OF MOLECULES **
C ** REAL RX(N),RY(N),RZ(N) MOLECULAR POSITIONS **
C ** REAL FX(N),FY(N),FZ(N) MOLECULAR FORCES **
C ** REAL BOX SIMULATION BOX LENGTH **
C ** REAL RCUT PAIR POTENTIAL CUTOFF **
C ** REAL V POTENTIAL ENERGY **
C ** REAL VC SHIFTED POTENTIAL **
C ** REAL W VIRIAL FUNCTION **
C ** REAL VIJ PAIR POTENTIAL BETWEEN I AND J **
C ** REAL WIJ NEGATIVE OF PAIR VIRIAL FUNCTION W **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
REAL RCUT, BOX, V, VC, W
REAL RX(N), RY(N), RZ(N), VX(N), VY(N), VZ(N)
REAL AX(N), AY(N), AZ(N), BX(N), BY(N), BZ(N)
REAL CX(N), CY(N), CZ(N), FX(N), FY(N), FZ(N)
INTEGER I, J, NCUT
REAL BOXINV, RCUTSQ
REAL RXI, RYI, RZI, FXI, FYI, FZI
REAL RXIJ, RYIJ, RZIJ, FXIJ, FYIJ, FZIJ
REAL RIJSQ, SR2, SR6, SR12, VIJ, WIJ, FIJ
C *******************************************************************
C ** USEFUL QUANTITIES **
BOXINV = 1.0 / BOX
RCUTSQ = RCUT ** 2
C ** ZERO FORCES, POTENTIAL, VIRIAL **
DO 100 I = 1, N
FX(I) = 0.0
FY(I) = 0.0
FZ(I) = 0.0
100 CONTINUE
NCUT = 0
V = 0.0
W = 0.0
C ** OUTER LOOP BEGINS **
DO 200 I = 1, N - 1
RXI = RX(I)
RYI = RY(I)
RZI = RZ(I)
FXI = FX(I)
FYI = FY(I)
FZI = FZ(I)
C ** INNER LOOP BEGINS **
DO 199 J = I + 1, N
RXIJ = RXI - RX(J)
RYIJ = RYI - RY(J)
RZIJ = RZI - RZ(J)
RXIJ = RXIJ - ANINT ( RXIJ * BOXINV ) * BOX
RYIJ = RYIJ - ANINT ( RYIJ * BOXINV ) * BOX
RZIJ = RZIJ - ANINT ( RZIJ * BOXINV ) * BOX
RIJSQ = RXIJ ** 2 + RYIJ ** 2 + RZIJ ** 2
IF ( RIJSQ .LT. RCUTSQ ) THEN
SR2 = 1.0 / RIJSQ
SR6 = SR2 * SR2 * SR2
SR12 = SR6 ** 2
VIJ = SR12 - SR6
V = V + VIJ
WIJ = VIJ + SR12
W = W + WIJ
FIJ = WIJ * SR2
FXIJ = FIJ * RXIJ
FYIJ = FIJ * RYIJ
FZIJ = FIJ * RZIJ
FXI = FXI + FXIJ
FYI = FYI + FYIJ
FZI = FZI + FZIJ
FX(J) = FX(J) - FXIJ
FY(J) = FY(J) - FYIJ
FZ(J) = FZ(J) - FZIJ
NCUT = NCUT + 1
ENDIF
199 CONTINUE
C ** INNER LOOP ENDS **
FX(I) = FXI
FY(I) = FYI
FZ(I) = FZI
200 CONTINUE
C ** OUTER LOOP ENDS **
C ** CALCULATE SHIFTED POTENTIAL **
SR2 = 1.0 / RCUTSQ
SR6 = SR2 * SR2 * SR2
SR12 = SR6 * SR6
VIJ = SR12 - SR6
VC = V - REAL ( NCUT ) * VIJ
C ** MULTIPLY RESULTS BY NUMERICAL FACTORS **
DO 300 I = 1, N
FX(I) = FX(I) * 24.0
FY(I) = FY(I) * 24.0
FZ(I) = FZ(I) * 24.0
300 CONTINUE
V = V * 4.0
VC = VC * 4.0
W = W * 24.0 / 3.0
RETURN
END
SUBROUTINE KINET ( K )
COMMON / BLOCK1 / RX, RY, RZ, VX, VY, VZ, AX, AY, AZ,
: BX, BY, BZ, CX, CY, CZ, FX, FY, FZ
COMMON / BLOCK2 / S, SV, SA, SB, SC, SF
C *******************************************************************
C ** ROUTINE TO COMPUTE KINETIC ENERGY IN NOSE METHOD **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
REAL K
REAL RX(N), RY(N), RZ(N), VX(N), VY(N), VZ(N)
REAL AX(N), AY(N), AZ(N), BX(N), BY(N), BZ(N)
REAL CX(N), CY(N), CZ(N), FX(N), FY(N), FZ(N)
REAL S, SV, SA, SB, SC, SF
INTEGER I
C *******************************************************************
K = 0.0
DO 1000 I = 1, N
K = K + VX(I) ** 2 + VY(I) ** 2 + VZ(I) ** 2
1000 CONTINUE
K = 0.5 * ( S ** 2 ) * K
RETURN
END
SUBROUTINE READCN ( CNFILE, BOX )
COMMON / BLOCK1 / RX, RY, RZ, VX, VY, VZ, AX, AY, AZ,
: BX, BY, BZ, CX, CY, CZ, FX, FY, FZ
COMMON / BLOCK2 / S, SV, SA, SB, SC, SF
C *******************************************************************
C ** SUBROUTINE TO READ IN INITIAL CONFIGURATION FROM UNIT 10 **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
CHARACTER CNFILE*(*)
REAL BOX
REAL RX(N), RY(N), RZ(N), VX(N), VY(N), VZ(N)
REAL AX(N), AY(N), AZ(N), BX(N), BY(N), BZ(N)
REAL CX(N), CY(N), CZ(N), FX(N), FY(N), FZ(N)
REAL S, SV, SA, SB, SC, SF
INTEGER CNUNIT, NN
PARAMETER ( CNUNIT = 10 )
C ******************************************************************
OPEN ( UNIT = CNUNIT, FILE = CNFILE,
: STATUS= 'OLD', FORM = 'UNFORMATTED' )
READ ( CNUNIT ) NN, BOX, S, SV, SA, SB, SC
IF ( NN .NE. N ) STOP ' INCORRECT NUMBER OF ATOMS '
READ ( CNUNIT ) RX, RY, RZ
READ ( CNUNIT ) VX, VY, VZ
READ ( CNUNIT ) AX, AY, AZ
READ ( CNUNIT ) BX, BY, BZ
READ ( CNUNIT ) CX, CY, CZ
CLOSE ( UNIT = CNUNIT )
RETURN
END
SUBROUTINE WRITCN ( CNFILE, BOX )
COMMON / BLOCK1 / RX, RY, RZ, VX, VY, VZ, AX, AY, AZ,
: BX, BY, BZ, CX, CY, CZ, FX, FY, FZ
COMMON / BLOCK2 / S, SV, SA, SB, SC, SF
C *******************************************************************
C ** ROUTINE TO WRITE OUT FINAL CONFIGURATION **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
CHARACTER CNFILE*(*)
REAL BOX
REAL RX(N), RY(N), RZ(N), VX(N), VY(N), VZ(N)
REAL AX(N), AY(N), AZ(N), BX(N), BY(N), BZ(N)
REAL CX(N), CY(N), CZ(N), FX(N), FY(N), FZ(N)
REAL S, SV, SA, SB, SC, SF
INTEGER CNUNIT
PARAMETER ( CNUNIT = 10 )
C ****************************************************************
OPEN ( UNIT = CNUNIT, FILE = CNFILE,
: STATUS='OLD', FORM = 'UNFORMATTED' )
WRITE ( CNUNIT ) N, BOX, S, SV, SA, SB, SC
WRITE ( CNUNIT ) RX, RY, RZ
WRITE ( CNUNIT ) VX, VY, VZ
WRITE ( CNUNIT ) AX, AY, AZ
WRITE ( CNUNIT ) BX, BY, BZ
WRITE ( CNUNIT ) CX, CY, CZ
CLOSE ( UNIT = CNUNIT )
RETURN
END
SUBROUTINE PREDIC ( DT )
COMMON / BLOCK1 / RX, RY, RZ, VX, VY, VZ, AX, AY, AZ,
: BX, BY, BZ, CX, CY, CZ, FX, FY, FZ
COMMON / BLOCK2 / S, SV, SA, SB, SC, SF
C *******************************************************************
C ** STANDARD TAYLOR SERIES PREDICTORS **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
REAL RX(N), RY(N), RZ(N), VX(N), VY(N), VZ(N)
REAL AX(N), AY(N), AZ(N), BX(N), BY(N), BZ(N)
REAL CX(N), CY(N), CZ(N), FX(N), FY(N), FZ(N)
REAL S, SV, SA, SB, SC, SF
REAL DT
INTEGER I
REAL C1, C2, C3, C4
C *******************************************************************
C1 = DT
C2 = C1 * DT / 2.0
C3 = C2 * DT / 3.0
C4 = C3 * DT / 4.0
DO 100 I = 1, N
RX(I) = RX(I) + C1*VX(I) + C2*AX(I) + C3*BX(I) + C4*CX(I)
RY(I) = RY(I) + C1*VY(I) + C2*AY(I) + C3*BY(I) + C4*CY(I)
RZ(I) = RZ(I) + C1*VZ(I) + C2*AZ(I) + C3*BZ(I) + C4*CZ(I)
VX(I) = VX(I) + C1*AX(I) + C2*BX(I) + C3*CX(I)
VY(I) = VY(I) + C1*AY(I) + C2*BY(I) + C3*CY(I)
VZ(I) = VZ(I) + C1*AZ(I) + C2*BZ(I) + C3*CZ(I)
AX(I) = AX(I) + C1*BX(I) + C2*CX(I)
AY(I) = AY(I) + C1*BY(I) + C2*CY(I)
AZ(I) = AZ(I) + C1*BZ(I) + C2*CZ(I)
BX(I) = BX(I) + C1*CX(I)
BY(I) = BY(I) + C1*CY(I)
BZ(I) = BZ(I) + C1*CZ(I)
100 CONTINUE
S = S + C1*SV + C2*SA + C3*SB + C4*SC
SV = SV + C1*SA + C2*SB + C3*SC
SA = SA + C1*SB + C2*SC
SB = SB + C1*SC
RETURN
END
SUBROUTINE CORREC ( DT )
COMMON / BLOCK1 / RX, RY, RZ, VX, VY, VZ, AX, AY, AZ,
: BX, BY, BZ, CX, CY, CZ, FX, FY, FZ
COMMON / BLOCK2 / S, SV, SA, SB, SC, SF
C *******************************************************************
C ** GEAR CORRECTOR ALGORITHM **
C ** **
C ** WE USE GEAR'S ALTERNATIVE COEFFICIENT GEAR0 WHICH APPLIES IN **
C ** THE CASE THAT FIRST TIME DERIVATIVES APPEAR ON THE RIGHT OF **
C ** THESE SECOND-ORDER DIFFERENTIAL EQUATIONS. **
C ** FOR TIMESTEP-SCALED VARIABLES THE COEFFICIENTS WOULD BE **
C ** 19/90, 3/4, 1, 1/2, 1/12. **
C ** **
C ** REFERENCES: **
C ** **
C ** GEAR, NUMERICAL INITIAL VALUE PROBLEMS IN ORDINARY **
C ** DIFFERENTIAL EQUATIONS (PRENTICE-HALL, 1971). **
C ** GEAR, REPORT ANL 7126 (ARGONNE NATIONAL LAB., 1966). **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
REAL RX(N), RY(N), RZ(N), VX(N), VY(N), VZ(N)
REAL AX(N), AY(N), AZ(N), BX(N), BY(N), BZ(N)
REAL CX(N), CY(N), CZ(N), FX(N), FY(N), FZ(N)
REAL S, SV, SA, SB, SC, SF
REAL DT
INTEGER I
REAL C1, C2, C3, C4
REAL CR, CV, CB, CC
REAL CORR, CORRX, CORRY, CORRZ
REAL AXI, AYI, AZI
REAL GEAR0, GEAR1, GEAR3, GEAR4
PARAMETER ( GEAR0 = 19.0 / 90.0, GEAR1 = 3.0 /4.0,
: GEAR3 = 1.0 / 2.0, GEAR4 = 1.0 /12.0 )
C *******************************************************************
C1 = DT
C2 = C1 * DT / 2.0
C3 = C2 * DT / 3.0
C4 = C3 * DT / 4.0
CR = GEAR0 * C2
CV = GEAR1 * C2 / C1
CB = GEAR3 * C2 / C3
CC = GEAR4 * C2 / C4
DO 400 I = 1, N
AXI = FX(I) / ( S ** 2 ) - 2.0 * SV * VX(I) / S
AYI = FY(I) / ( S ** 2 ) - 2.0 * SV * VY(I) / S
AZI = FZ(I) / ( S ** 2 ) - 2.0 * SV * VZ(I) / S
CORRX = AXI - AX(I)
CORRY = AYI - AY(I)
CORRZ = AZI - AZ(I)
RX(I) = RX(I) + CR * CORRX
RY(I) = RY(I) + CR * CORRY
RZ(I) = RZ(I) + CR * CORRZ
VX(I) = VX(I) + CV * CORRX
VY(I) = VY(I) + CV * CORRY
VZ(I) = VZ(I) + CV * CORRZ
AX(I) = AXI
AY(I) = AYI
AZ(I) = AZI
BX(I) = BX(I) + CB * CORRX
BY(I) = BY(I) + CB * CORRY
BZ(I) = BZ(I) + CB * CORRZ
CX(I) = CX(I) + CC * CORRX
CY(I) = CY(I) + CC * CORRY
CZ(I) = CZ(I) + CC * CORRZ
400 CONTINUE
CORR = SF - SA
S = S + CR * CORR
SV = SV + CV * CORR
SA = SF
SB = SB + CB * CORR
SC = SC + CC * CORR
RETURN
END