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47 lines
1.6 KiB
Fortran
47 lines
1.6 KiB
Fortran
*DECK CATAN2
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COMPLEX FUNCTION CATAN2 (CSN, CCS)
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C***BEGIN PROLOGUE CATAN2
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C***PURPOSE Compute the complex arc tangent in the proper quadrant.
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C***LIBRARY SLATEC (FNLIB)
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C***CATEGORY C4A
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C***TYPE COMPLEX (CATAN2-C)
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C***KEYWORDS ARC TANGENT, ELEMENTARY FUNCTIONS, FNLIB, POLAR ANGEL,
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C QUADRANT, TRIGONOMETRIC
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C***AUTHOR Fullerton, W., (LANL)
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C***DESCRIPTION
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C
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C CATAN2(CSN,CCS) calculates the complex trigonometric arc
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C tangent of the ratio CSN/CCS and returns a result whose real
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C part is in the correct quadrant (within a multiple of 2*PI). The
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C result is in units of radians and the real part is between -PI
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C and +PI.
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C
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C***REFERENCES (NONE)
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C***ROUTINES CALLED CATAN, XERMSG
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C***REVISION HISTORY (YYMMDD)
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C 770401 DATE WRITTEN
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C 890531 Changed all specific intrinsics to generic. (WRB)
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C 890531 REVISION DATE from Version 3.2
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
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C 900326 Removed duplicate information from DESCRIPTION section.
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C (WRB)
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C***END PROLOGUE CATAN2
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COMPLEX CSN, CCS, CATAN
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SAVE PI
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DATA PI / 3.1415926535 8979323846E0 /
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C***FIRST EXECUTABLE STATEMENT CATAN2
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IF (ABS(CCS).EQ.0.) GO TO 10
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C
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CATAN2 = CATAN (CSN/CCS)
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IF (REAL(CCS).LT.0.) CATAN2 = CATAN2 + PI
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IF (REAL(CATAN2).GT.PI) CATAN2 = CATAN2 - 2.0*PI
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RETURN
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C
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10 IF (ABS(CSN) .EQ. 0.) CALL XERMSG ('SLATEC', 'CATAN2',
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+ 'CALLED WITH BOTH ARGUMENTS ZERO', 1, 2)
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C
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CATAN2 = CMPLX (SIGN(0.5*PI,REAL(CSN)), 0.0)
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C
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RETURN
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END
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