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65 lines
2.2 KiB
Fortran
65 lines
2.2 KiB
Fortran
*DECK DDATRP
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SUBROUTINE DDATRP (X, XOUT, YOUT, YPOUT, NEQ, KOLD, PHI, PSI)
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C***BEGIN PROLOGUE DDATRP
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C***SUBSIDIARY
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C***PURPOSE Interpolation routine for DDASSL.
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C***LIBRARY SLATEC (DASSL)
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C***TYPE DOUBLE PRECISION (SDATRP-S, DDATRP-D)
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C***AUTHOR Petzold, Linda R., (LLNL)
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C***DESCRIPTION
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C-----------------------------------------------------------------------
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C THE METHODS IN SUBROUTINE DDASTP USE POLYNOMIALS
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C TO APPROXIMATE THE SOLUTION. DDATRP APPROXIMATES THE
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C SOLUTION AND ITS DERIVATIVE AT TIME XOUT BY EVALUATING
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C ONE OF THESE POLYNOMIALS, AND ITS DERIVATIVE,THERE.
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C INFORMATION DEFINING THIS POLYNOMIAL IS PASSED FROM
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C DDASTP, SO DDATRP CANNOT BE USED ALONE.
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C
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C THE PARAMETERS ARE:
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C X THE CURRENT TIME IN THE INTEGRATION.
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C XOUT THE TIME AT WHICH THE SOLUTION IS DESIRED
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C YOUT THE INTERPOLATED APPROXIMATION TO Y AT XOUT
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C (THIS IS OUTPUT)
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C YPOUT THE INTERPOLATED APPROXIMATION TO YPRIME AT XOUT
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C (THIS IS OUTPUT)
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C NEQ NUMBER OF EQUATIONS
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C KOLD ORDER USED ON LAST SUCCESSFUL STEP
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C PHI ARRAY OF SCALED DIVIDED DIFFERENCES OF Y
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C PSI ARRAY OF PAST STEPSIZE HISTORY
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C-----------------------------------------------------------------------
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C***ROUTINES CALLED (NONE)
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C***REVISION HISTORY (YYMMDD)
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C 830315 DATE WRITTEN
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C 901009 Finished conversion to SLATEC 4.0 format (F.N.Fritsch)
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C 901019 Merged changes made by C. Ulrich with SLATEC 4.0 format.
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C 901026 Added explicit declarations for all variables and minor
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C cosmetic changes to prologue. (FNF)
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C***END PROLOGUE DDATRP
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C
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INTEGER NEQ, KOLD
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DOUBLE PRECISION X, XOUT, YOUT(*), YPOUT(*), PHI(NEQ,*), PSI(*)
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C
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INTEGER I, J, KOLDP1
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DOUBLE PRECISION C, D, GAMMA, TEMP1
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C
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C***FIRST EXECUTABLE STATEMENT DDATRP
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KOLDP1=KOLD+1
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TEMP1=XOUT-X
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DO 10 I=1,NEQ
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YOUT(I)=PHI(I,1)
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10 YPOUT(I)=0.0D0
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C=1.0D0
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D=0.0D0
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GAMMA=TEMP1/PSI(1)
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DO 30 J=2,KOLDP1
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D=D*GAMMA+C/PSI(J-1)
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C=C*GAMMA
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GAMMA=(TEMP1+PSI(J-1))/PSI(J)
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DO 20 I=1,NEQ
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YOUT(I)=YOUT(I)+C*PHI(I,J)
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20 YPOUT(I)=YPOUT(I)+D*PHI(I,J)
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30 CONTINUE
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RETURN
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C
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C------END OF SUBROUTINE DDATRP------
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END
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