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52 lines
1.7 KiB
52 lines
1.7 KiB
2 years ago
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C Copyright(C) 1999-2020 National Technology & Engineering Solutions
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C of Sandia, LLC (NTESS). Under the terms of Contract DE-NA0003525 with
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C NTESS, the U.S. Government retains certain rights in this software.
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C
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C See packages/seacas/LICENSE for details
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C======================================================================
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SUBROUTINE BS(N,S,F,L,X)
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C**********************************************************************
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C Subroutine BS does the back substitution for the soultion of the
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C local least squares extrapolation technique for element variables
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C from their element centroid location to a nodal location.
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C The least squares solution is started by a Gauss elimination in
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C subroutine FRGE. The process is started in subroutines EXTQ for
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C 4-node quads or EXTH for 8-node hexes.
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C Called by EXTH, EXTQ
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C**********************************************************************
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C N INT number of equations - 1 + the number of dimensions
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C S REAL the coefficient matrix - after forward gauss elimination
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C F REAL the load vector
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C L INT dummy array - placeholder for subscripts
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C X REAL the solution vector - coefficients of the equation
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C SUM REAL dummy variable - used in the solution scheme
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C**********************************************************************
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C subroutine written in double precision
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DOUBLE PRECISION S(N,N),F(N),X(N),SUM
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INTEGER L(N)
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DO 3 K = 1,N-1
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DO 2 I = K+1,N
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F(L(I)) = F(L(I)) - S(L(I),K) * F(L(K))
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2 CONTINUE
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3 CONTINUE
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X(N) = F(L(N)) / S(L(N),N)
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DO 5 I = N-1,1,-1
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SUM = F(L(I))
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DO 4 J = I+1,N
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SUM = SUM - S(L(I),J) * X(J)
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4 CONTINUE
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X(I) = SUM / S(L(I),I)
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5 CONTINUE
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RETURN
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END
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