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39 lines
1.2 KiB
39 lines
1.2 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 SPLINE(X,Y,N,YP1,YPN,Y2)
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C=======================================================================
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PARAMETER (NMAX=100)
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DIMENSION X(N),Y(N),Y2(N),U(NMAX)
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IF (YP1.GT..99E30) THEN
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Y2(1)=0.
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U(1)=0.
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ELSE
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Y2(1)=-0.5
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U(1)=(3./(X(2)-X(1)))*((Y(2)-Y(1))/(X(2)-X(1))-YP1)
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ENDIF
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DO 11 I=2,N-1
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SIG=(X(I)-X(I-1))/(X(I+1)-X(I-1))
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P=SIG*Y2(I-1)+2.
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Y2(I)=(SIG-1.)/P
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U(I)=(6.*((Y(I+1)-Y(I))/(X(I+1)-X(I))-(Y(I)-Y(I-1))
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* /(X(I)-X(I-1)))/(X(I+1)-X(I-1))-SIG*U(I-1))/P
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11 CONTINUE
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IF (YPN.GT..99E30) THEN
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QN=0.
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UN=0.
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ELSE
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QN=0.5
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UN=(3./(X(N)-X(N-1)))*(YPN-(Y(N)-Y(N-1))/(X(N)-X(N-1)))
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ENDIF
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Y2(N)=(UN-QN*U(N-1))/(QN*Y2(N-1)+1.)
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DO 12 K=N-1,1,-1
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Y2(K)=Y2(K)*Y2(K+1)+U(K)
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12 CONTINUE
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RETURN
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END
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