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83 lines
2.4 KiB
Fortran
83 lines
2.4 KiB
Fortran
*DECK DXQMU
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SUBROUTINE DXQMU (NU1, NU2, MU1, MU2, THETA, X, SX, ID, PQA, IPQA,
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1 IERROR)
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C***BEGIN PROLOGUE DXQMU
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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 Method: forward mu-wise recurrence for Q(MU,NU,X) for fixed
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C nu to obtain Q(MU1,NU,X), Q(MU1+1,NU,X), ..., Q(MU2,NU,X).
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C***LIBRARY SLATEC
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C***CATEGORY C3A2, C9
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C***TYPE DOUBLE PRECISION (XQMU-S, DXQMU-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 DXADD, DXADJ, DXPQNU
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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 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 DXQMU
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DIMENSION PQA(*),IPQA(*)
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DOUBLE PRECISION DMU,NU,NU1,NU2,PQ,PQA,PQ1,PQ2,SX,X,X1,X2
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DOUBLE PRECISION THETA
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C***FIRST EXECUTABLE STATEMENT DXQMU
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IERROR=0
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MU=0
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C
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C CALL DXPQNU TO OBTAIN Q(0.,NU1,X)
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C
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CALL DXPQNU(NU1,NU2,MU,THETA,ID,PQA,IPQA,IERROR)
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IF (IERROR.NE.0) RETURN
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PQ2=PQA(1)
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IPQ2=IPQA(1)
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MU=1
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C
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C CALL DXPQNU TO OBTAIN Q(1.,NU1,X)
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C
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CALL DXPQNU(NU1,NU2,MU,THETA,ID,PQA,IPQA,IERROR)
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IF (IERROR.NE.0) RETURN
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NU=NU1
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K=0
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MU=1
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DMU=1.D0
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PQ1=PQA(1)
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IPQ1=IPQA(1)
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IF(MU1.GT.0) GO TO 310
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K=K+1
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PQA(K)=PQ2
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IPQA(K)=IPQ2
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IF(MU2.LT.1) GO TO 330
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310 IF(MU1.GT.1) GO TO 320
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K=K+1
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PQA(K)=PQ1
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IPQA(K)=IPQ1
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IF(MU2.LE.1) GO TO 330
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320 CONTINUE
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C
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C FORWARD RECURRENCE IN MU TO OBTAIN
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C Q(MU1,NU,X),Q(MU1+1,NU,X),....,Q(MU2,NU,X) USING
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C Q(MU+1,NU,X)=-2.*MU*X*SQRT(1./(1.-X**2))*Q(MU,NU,X)
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C -(NU+MU)*(NU-MU+1.)*Q(MU-1,NU,X)
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C
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X1=-2.D0*DMU*X*SX*PQ1
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X2=(NU+DMU)*(NU-DMU+1.D0)*PQ2
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CALL DXADD(X1,IPQ1,-X2,IPQ2,PQ,IPQ,IERROR)
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IF (IERROR.NE.0) RETURN
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CALL DXADJ(PQ,IPQ,IERROR)
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IF (IERROR.NE.0) RETURN
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PQ2=PQ1
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IPQ2=IPQ1
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PQ1=PQ
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IPQ1=IPQ
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MU=MU+1
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DMU=DMU+1.D0
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IF(MU.LT.MU1) GO TO 320
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K=K+1
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PQA(K)=PQ
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IPQA(K)=IPQ
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IF(MU2.GT.MU) GO TO 320
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330 RETURN
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END
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