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68 lines
1.8 KiB
Fortran
68 lines
1.8 KiB
Fortran
*DECK TRIX
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SUBROUTINE TRIX (IDEGBR, IDEGCR, M, A, B, C, Y, TCOS, D, W)
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C***BEGIN PROLOGUE TRIX
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C***SUBSIDIARY
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C***PURPOSE Subsidiary to GENBUN
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C***LIBRARY SLATEC
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C***TYPE SINGLE PRECISION (TRIX-S, CMPTRX-C)
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C***AUTHOR (UNKNOWN)
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C***DESCRIPTION
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C
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C Subroutine to solve a system of linear equations where the
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C coefficient matrix is a rational function in the matrix given by
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C TRIDIAGONAL ( . . . , A(I), B(I), C(I), . . . ).
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C
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C***SEE ALSO GENBUN
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C***ROUTINES CALLED (NONE)
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C***REVISION HISTORY (YYMMDD)
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C 801001 DATE WRITTEN
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900402 Added TYPE section. (WRB)
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C***END PROLOGUE TRIX
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C
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DIMENSION A(*) ,B(*) ,C(*) ,Y(*) ,
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1 TCOS(*) ,D(*) ,W(*)
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INTEGER KB, KC
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C***FIRST EXECUTABLE STATEMENT TRIX
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MM1 = M-1
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KB = IDEGBR+1
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KC = IDEGCR+1
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L = (IDEGBR+1)/(IDEGCR+1)
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LINT = 1
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DO 108 K=1,IDEGBR
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X = TCOS(K)
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IF (K .NE. L) GO TO 102
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I = IDEGBR+LINT
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XX = X-TCOS(I)
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DO 101 I=1,M
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W(I) = Y(I)
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Y(I) = XX*Y(I)
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101 CONTINUE
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102 CONTINUE
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Z = 1./(B(1)-X)
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D(1) = C(1)*Z
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Y(1) = Y(1)*Z
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DO 103 I=2,MM1
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Z = 1./(B(I)-X-A(I)*D(I-1))
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D(I) = C(I)*Z
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Y(I) = (Y(I)-A(I)*Y(I-1))*Z
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103 CONTINUE
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Z = B(M)-X-A(M)*D(MM1)
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IF (Z .NE. 0.) GO TO 104
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Y(M) = 0.
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GO TO 105
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104 Y(M) = (Y(M)-A(M)*Y(MM1))/Z
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105 CONTINUE
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DO 106 IP=1,MM1
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I = M-IP
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Y(I) = Y(I)-D(I)*Y(I+1)
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106 CONTINUE
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IF (K .NE. L) GO TO 108
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DO 107 I=1,M
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Y(I) = Y(I)+W(I)
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107 CONTINUE
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LINT = LINT+1
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L = (LINT*KB)/KC
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108 CONTINUE
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RETURN
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END
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