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