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Last change
on this file since 1940 was
1289,
checked in by Ehouarn Millour, 15 years ago
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Minor improvement: Bring Jacobi into the XXIst century.
Routine can now handle matix of any size (tested on local Linux machines and IBM Power6 that this doesn't change results compared to old version).
EM
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-
Property svn:eol-style set to
native
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Property svn:keywords set to
Author Date Id Revision
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File size:
2.7 KB
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| 1 | ! |
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| 2 | ! $Id: jacobi.F90 1289 2009-12-18 14:51:22Z jghattas $ |
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| 3 | ! |
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| 4 | SUBROUTINE JACOBI(A,N,NP,D,V,NROT) |
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| 5 | implicit none |
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| 6 | ! Arguments: |
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| 7 | integer,intent(in) :: N |
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| 8 | integer,intent(in) :: NP |
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| 9 | integer,intent(out) :: NROT |
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| 10 | real,intent(inout) :: A(NP,NP) |
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| 11 | real,intent(out) :: D(NP) |
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| 12 | real,intent(out) :: V(NP,NP) |
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| 13 | |
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| 14 | ! local variables: |
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| 15 | integer :: IP,IQ,I,J |
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| 16 | real :: SM,TRESH,G,H,T,THETA,C,S,TAU |
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| 17 | real :: B(N) |
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| 18 | real :: Z(N) |
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| 19 | |
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| 20 | DO IP=1,N |
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| 21 | DO IQ=1,N |
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| 22 | V(IP,IQ)=0. |
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| 23 | ENDDO |
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| 24 | V(IP,IP)=1. |
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| 25 | ENDDO |
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| 26 | DO IP=1,N |
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| 27 | B(IP)=A(IP,IP) |
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| 28 | D(IP)=B(IP) |
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| 29 | Z(IP)=0. |
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| 30 | ENDDO |
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| 31 | NROT=0 |
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| 32 | DO I=1,50 ! 50? I suspect this should be NP |
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| 33 | ! but convergence is fast enough anyway |
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| 34 | SM=0. |
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| 35 | DO IP=1,N-1 |
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| 36 | DO IQ=IP+1,N |
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| 37 | SM=SM+ABS(A(IP,IQ)) |
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| 38 | ENDDO |
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| 39 | ENDDO |
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| 40 | IF(SM.EQ.0.)RETURN |
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| 41 | IF(I.LT.4)THEN |
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| 42 | TRESH=0.2*SM/N**2 |
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| 43 | ELSE |
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| 44 | TRESH=0. |
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| 45 | ENDIF |
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| 46 | DO IP=1,N-1 |
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| 47 | DO IQ=IP+1,N |
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| 48 | G=100.*ABS(A(IP,IQ)) |
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| 49 | IF((I.GT.4).AND.(ABS(D(IP))+G.EQ.ABS(D(IP))) & |
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| 50 | .AND.(ABS(D(IQ))+G.EQ.ABS(D(IQ))))THEN |
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| 51 | A(IP,IQ)=0. |
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| 52 | ELSE IF(ABS(A(IP,IQ)).GT.TRESH)THEN |
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| 53 | H=D(IQ)-D(IP) |
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| 54 | IF(ABS(H)+G.EQ.ABS(H))THEN |
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| 55 | T=A(IP,IQ)/H |
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| 56 | ELSE |
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| 57 | THETA=0.5*H/A(IP,IQ) |
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| 58 | T=1./(ABS(THETA)+SQRT(1.+THETA**2)) |
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| 59 | IF(THETA.LT.0.)T=-T |
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| 60 | ENDIF |
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| 61 | C=1./SQRT(1+T**2) |
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| 62 | S=T*C |
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| 63 | TAU=S/(1.+C) |
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| 64 | H=T*A(IP,IQ) |
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| 65 | Z(IP)=Z(IP)-H |
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| 66 | Z(IQ)=Z(IQ)+H |
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| 67 | D(IP)=D(IP)-H |
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| 68 | D(IQ)=D(IQ)+H |
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| 69 | A(IP,IQ)=0. |
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| 70 | DO J=1,IP-1 |
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| 71 | G=A(J,IP) |
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| 72 | H=A(J,IQ) |
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| 73 | A(J,IP)=G-S*(H+G*TAU) |
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| 74 | A(J,IQ)=H+S*(G-H*TAU) |
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| 75 | ENDDO |
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| 76 | DO J=IP+1,IQ-1 |
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| 77 | G=A(IP,J) |
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| 78 | H=A(J,IQ) |
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| 79 | A(IP,J)=G-S*(H+G*TAU) |
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| 80 | A(J,IQ)=H+S*(G-H*TAU) |
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| 81 | ENDDO |
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| 82 | DO J=IQ+1,N |
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| 83 | G=A(IP,J) |
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| 84 | H=A(IQ,J) |
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| 85 | A(IP,J)=G-S*(H+G*TAU) |
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| 86 | A(IQ,J)=H+S*(G-H*TAU) |
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| 87 | ENDDO |
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| 88 | DO J=1,N |
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| 89 | G=V(J,IP) |
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| 90 | H=V(J,IQ) |
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| 91 | V(J,IP)=G-S*(H+G*TAU) |
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| 92 | V(J,IQ)=H+S*(G-H*TAU) |
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| 93 | ENDDO |
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| 94 | NROT=NROT+1 |
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| 95 | ENDIF |
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| 96 | ENDDO |
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| 97 | ENDDO |
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| 98 | DO IP=1,N |
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| 99 | B(IP)=B(IP)+Z(IP) |
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| 100 | D(IP)=B(IP) |
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| 101 | Z(IP)=0. |
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| 102 | ENDDO |
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| 103 | ENDDO ! of DO I=1,50 |
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| 104 | STOP 'Jacobi: 50 iterations should never happen' |
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| 105 | RETURN |
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| 106 | END SUBROUTINE JACOBI |
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