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76 lines
2.4 KiB
Fortran
76 lines
2.4 KiB
Fortran
*DECK DXPMUP
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SUBROUTINE DXPMUP (NU1, NU2, MU1, MU2, PQA, IPQA, IERROR)
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C***BEGIN PROLOGUE DXPMUP
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C***SUBSIDIARY
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C***PURPOSE To compute the values of Legendre functions for DXLEGF.
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C This subroutine transforms an array of Legendre functions
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C of the first kind of negative order stored in array PQA
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C into Legendre functions of the first kind of positive
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C order stored in array PQA. The original array is destroyed.
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C***LIBRARY SLATEC
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C***CATEGORY C3A2, C9
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C***TYPE DOUBLE PRECISION (XPMUP-S, DXPMUP-D)
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C***KEYWORDS LEGENDRE FUNCTIONS
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C***AUTHOR Smith, John M., (NBS and George Mason University)
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C***ROUTINES CALLED DXADJ
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C***REVISION HISTORY (YYMMDD)
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C 820728 DATE WRITTEN
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C 890126 Revised to meet SLATEC CML recommendations. (DWL and JMS)
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C 901019 Revisions to prologue. (DWL and WRB)
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C 901106 Changed all specific intrinsics to generic. (WRB)
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C Corrected order of sections in prologue and added TYPE
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C section. (WRB)
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C 920127 Revised PURPOSE section of prologue. (DWL)
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C***END PROLOGUE DXPMUP
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DOUBLE PRECISION DMU,NU,NU1,NU2,PQA,PROD
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DIMENSION PQA(*),IPQA(*)
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C***FIRST EXECUTABLE STATEMENT DXPMUP
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IERROR=0
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NU=NU1
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MU=MU1
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DMU=MU
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N=INT(NU2-NU1+.1D0)+(MU2-MU1)+1
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J=1
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IF(MOD(REAL(NU),1.).NE.0.) GO TO 210
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200 IF(DMU.LT.NU+1.D0) GO TO 210
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PQA(J)=0.D0
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IPQA(J)=0
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J=J+1
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IF(J.GT.N) RETURN
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C INCREMENT EITHER MU OR NU AS APPROPRIATE.
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IF(NU2-NU1.GT..5D0) NU=NU+1.D0
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IF(MU2.GT.MU1) MU=MU+1
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GO TO 200
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C
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C TRANSFORM P(-MU,NU,X) TO P(MU,NU,X) USING
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C P(MU,NU,X)=(NU-MU+1)*(NU-MU+2)*...*(NU+MU)*P(-MU,NU,X)*(-1)**MU
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C
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210 PROD=1.D0
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IPROD=0
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K=2*MU
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IF(K.EQ.0) GO TO 222
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DO 220 L=1,K
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PROD=PROD*(DMU-NU-L)
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220 CALL DXADJ(PROD,IPROD,IERROR)
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IF (IERROR.NE.0) RETURN
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222 CONTINUE
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DO 240 I=J,N
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IF(MU.EQ.0) GO TO 225
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PQA(I)=PQA(I)*PROD*(-1)**MU
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IPQA(I)=IPQA(I)+IPROD
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CALL DXADJ(PQA(I),IPQA(I),IERROR)
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IF (IERROR.NE.0) RETURN
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225 IF(NU2-NU1.GT..5D0) GO TO 230
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PROD=(DMU-NU)*PROD*(-DMU-NU-1.D0)
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CALL DXADJ(PROD,IPROD,IERROR)
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IF (IERROR.NE.0) RETURN
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MU=MU+1
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DMU=DMU+1.D0
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GO TO 240
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230 PROD=PROD*(-DMU-NU-1.D0)/(DMU-NU-1.D0)
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CALL DXADJ(PROD,IPROD,IERROR)
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IF (IERROR.NE.0) RETURN
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NU=NU+1.D0
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240 CONTINUE
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RETURN
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END
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