29 lines
772 B
Fortran
29 lines
772 B
Fortran
SUBROUTINE cyclic(a,b,c,alpha,beta,r,x,n)
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INTEGER n,NMAX
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REAL alpha,beta,a(n),b(n),c(n),r(n),x(n)
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PARAMETER (NMAX=500)
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CU USES tridag
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INTEGER i
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REAL fact,gamma,bb(NMAX),u(NMAX),z(NMAX)
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if(n.le.2)pause 'n too small in cyclic'
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if(n.gt.NMAX)pause 'NMAX too small in cyclic'
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gamma=-b(1)
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bb(1)=b(1)-gamma
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bb(n)=b(n)-alpha*beta/gamma
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do 11 i=2,n-1
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bb(i)=b(i)
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11 continue
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call tridag(a,bb,c,r,x,n)
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u(1)=gamma
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u(n)=alpha
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do 12 i=2,n-1
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u(i)=0.
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12 continue
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call tridag(a,bb,c,u,z,n)
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fact=(x(1)+beta*x(n)/gamma)/(1.+z(1)+beta*z(n)/gamma)
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do 13 i=1,n
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x(i)=x(i)-fact*z(i)
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13 continue
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return
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END
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