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C $Id: vctcnv.f 3304 2011-01-17 15:25:59Z brideout $
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C
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SUBROUTINE VCTCNV(FX,FY,FZ,X,Y,Z,FR,FT,FP,R,THETA,PHI,IMODE)
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C
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C jmh - 11/79 ans fortran 66
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C
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C VCTCNV converts between the cartesian and spherical coordinate
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C representations of a vector field f. (FX,FY,FZ) are the
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C components of the field at (X,Y,Z). (FR,FT,FP) are the
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C components of the field at (R,THETA,PHI) in the directions of
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C increasing R, increasing THETA and increasing PHI. if IMODE=1,
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C (FX,FY,FZ,X,Y,Z) -> (FR,FT,FP,R,THETA,PHI). if IMODE=2,
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C (FR,FT,FP,R,THETA,PHI) -> (FX,FY,FZ,X,Y,Z). THETA and PHI are
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C in degrees.
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C
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C Input:
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C IMODE - 1 cartesian to spherical
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C 2 spherical to cartesian
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C
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C Input, output:
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C FX,FY,FZ - cartesian vector field components
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C X,Y,Z - cartesian vector field coordinates
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C FR,FT,FP - spherical vector field components
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C R,THETA,PHI - spherical vector field coordinates
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C
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C .. Scalar Arguments ..
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DOUBLE PRECISION FP,FR,FT,FX,FY,FZ,PHI,R,THETA,X,Y,Z
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INTEGER IMODE
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C ..
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C .. Local Scalars ..
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DOUBLE PRECISION CP,CT,DTR,P,RHO2,RLMIN,SP,ST,T
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C ..
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C .. Intrinsic Functions ..
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INTRINSIC ABS,DATAN2,DCOS,DMAX1,DSIN,DSQRT,SIGN
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C ..
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C .. Data statements ..
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DATA DTR/.0174532925199D0/,RLMIN/1.D-38/
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C ..
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C
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IF (IMODE.EQ.2) THEN
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C
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T = DTR*THETA
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P = DTR*PHI
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CT = DCOS(T)
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ST = DSIN(T)
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CP = DCOS(P)
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SP = DSIN(P)
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X = R*ST*CP
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Y = R*ST*SP
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Z = R*CT
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FX = ST*CP*FR + CT*CP*FT - SP*FP
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FY = ST*SP*FR + CT*SP*FT + CP*FP
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FZ = CT*FR - ST*FT
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ELSE
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C
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RHO2 = X*X + Y*Y
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R = DSQRT(RHO2+Z*Z)
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THETA = DATAN2(DSQRT(RHO2),SIGN(1.D0,Z)*DMAX1(ABS(Z),RLMIN))
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PHI = DATAN2(Y,SIGN(1.D0,X)*DMAX1(ABS(X),RLMIN))
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CT = DCOS(THETA)
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ST = DSIN(THETA)
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CP = DCOS(PHI)
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SP = DSIN(PHI)
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THETA = THETA/DTR
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PHI = PHI/DTR
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FR = ST*CP*FX + ST*SP*FY + CT*FZ
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FT = CT*CP*FX + CT*SP*FY - ST*FZ
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FP = -SP*FX + CP*FY
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END IF
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RETURN
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C
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END
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