44 lines
938 B
Fortran
44 lines
938 B
Fortran
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SUBROUTINE LEGAUS(LL,X,W)
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C
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C GAUSS-LEGENDRE POINT AND WAIT ROUTINE FOR AN EVEN NO. OF POINTS
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C
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C ll = order i.e. the total number of points for -1< x <1
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C x = points
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C w = weights
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C
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IMPLICIT REAL*8(A-H,O-Z)
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real*4 x,w
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DIMENSION X(100),W(100)
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Z3=-1.6/FLOAT(LL+1)
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Z2=3.0*Z3
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Z1=5.0*Z3
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NL=(LL+1)/2
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DO 200 L=1,NL
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ZOLD=0.0
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Z=Z1+3.0*(Z3-Z2)
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DO 50 J=1,10
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P1=0.0
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P2=1.0
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DO 30 I=1,LL
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P3=(FLOAT(I+I-1)*Z*P2-FLOAT(I-1)*P1)/FLOAT(I)
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P1=P2
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P2=P3
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30 CONTINUE
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DP=FLOAT(LL)*(P1-Z*P2)/(1.0-Z*Z)
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Z=Z-P2/DP
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IF(ABS(Z-ZOLD)/Z.LT.1.0E-10) GO TO 51
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ZOLD=Z
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50 CONTINUE
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WRITE(6,9100)L
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9100 FORMAT(28H0NO CONVERGENCE FOR ZERO NO.,I4)
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51 CONTINUE
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X(L)=Z
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W(L)=2.0/((1.0-Z*Z)*DP*DP)
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Z1=Z2
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Z2=Z3
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Z3=Z
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200 CONTINUE
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RETURN
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END
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