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! $Header: /home/cvsroot/LMDZ4/libf/filtrez/jacobi.F,v 1.1.1.1 2004/05/19 |
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! 12:53:09 lmdzadmin Exp $ |
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SUBROUTINE jacobi(a, n, np, d, v, nrot) |
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implicit none |
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integer, PARAMETER:: nmax=400 |
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integer n, np |
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real a(np, np), d(np), v(np, np), b(nmax), z(nmax) |
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integer ip, iq, nrot, i, j |
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real sm, g, h, t, theta, c, s, tau, tresh |
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IF (n>nmax) THEN |
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PRINT *, 'n, nmax=', n, nmax |
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PRINT *, 'Surdimensionnement insuffisant dans jacobi' |
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STOP 1 |
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END IF |
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DO ip = 1, n |
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DO iq = 1, n |
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v(ip, iq) = 0. |
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END DO |
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v(ip, ip) = 1. |
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END DO |
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DO ip = 1, n |
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b(ip) = a(ip, ip) |
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d(ip) = b(ip) |
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z(ip) = 0. |
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END DO |
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nrot = 0 |
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DO i = 1, 50 |
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sm = 0. |
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DO ip = 1, n - 1 |
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DO iq = ip + 1, n |
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sm = sm + abs(a(ip,iq)) |
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END DO |
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END DO |
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IF (sm==0.) RETURN |
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IF (i<4) THEN |
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tresh = 0.2*sm/n**2 |
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ELSE |
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tresh = 0. |
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END IF |
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DO ip = 1, n - 1 |
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DO iq = ip + 1, n |
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g = 100.*abs(a(ip,iq)) |
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IF ((i>4) .AND. (abs(d(ip))+g==abs(d(ip))) .AND. (abs(d(iq))+g==abs( & |
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d(iq)))) THEN |
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a(ip, iq) = 0. |
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ELSE IF (abs(a(ip,iq))>tresh) THEN |
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h = d(iq) - d(ip) |
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IF (abs(h)+g==abs(h)) THEN |
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t = a(ip, iq)/h |
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ELSE |
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theta = 0.5*h/a(ip, iq) |
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t = 1./(abs(theta)+sqrt(1.+theta**2)) |
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IF (theta<0.) t = -t |
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END IF |
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c = 1./sqrt(1+t**2) |
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s = t*c |
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tau = s/(1.+c) |
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h = t*a(ip, iq) |
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z(ip) = z(ip) - h |
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z(iq) = z(iq) + h |
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d(ip) = d(ip) - h |
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d(iq) = d(iq) + h |
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a(ip, iq) = 0. |
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DO j = 1, ip - 1 |
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g = a(j, ip) |
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h = a(j, iq) |
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a(j, ip) = g - s*(h+g*tau) |
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a(j, iq) = h + s*(g-h*tau) |
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END DO |
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DO j = ip + 1, iq - 1 |
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g = a(ip, j) |
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h = a(j, iq) |
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a(ip, j) = g - s*(h+g*tau) |
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a(j, iq) = h + s*(g-h*tau) |
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END DO |
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DO j = iq + 1, n |
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g = a(ip, j) |
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h = a(iq, j) |
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a(ip, j) = g - s*(h+g*tau) |
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a(iq, j) = h + s*(g-h*tau) |
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END DO |
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DO j = 1, n |
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g = v(j, ip) |
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h = v(j, iq) |
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v(j, ip) = g - s*(h+g*tau) |
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v(j, iq) = h + s*(g-h*tau) |
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END DO |
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nrot = nrot + 1 |
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END IF |
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END DO |
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END DO |
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DO ip = 1, n |
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b(ip) = b(ip) + z(ip) |
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d(ip) = b(ip) |
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z(ip) = 0. |
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END DO |
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END DO |
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STOP '50 iterations should never happen' |
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RETURN |
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END SUBROUTINE jacobi |
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