*DECK ICAMAX INTEGER FUNCTION ICAMAX (N, CX, INCX) C***BEGIN PROLOGUE ICAMAX C***PURPOSE Find the smallest index of the component of a complex C vector having the maximum sum of magnitudes of real C and imaginary parts. C***LIBRARY SLATEC (BLAS) C***CATEGORY D1A2 C***TYPE COMPLEX (ISAMAX-S, IDAMAX-D, ICAMAX-C) C***KEYWORDS BLAS, LINEAR ALGEBRA, MAXIMUM COMPONENT, VECTOR C***AUTHOR Lawson, C. L., (JPL) C Hanson, R. J., (SNLA) C Kincaid, D. R., (U. of Texas) C Krogh, F. T., (JPL) C***DESCRIPTION C C B L A S Subprogram C Description of Parameters C C --Input-- C N number of elements in input vector(s) C CX complex vector with N elements C INCX storage spacing between elements of CX C C --Output-- C ICAMAX smallest index (zero if N .LE. 0) C C Returns the smallest index of the component of CX having the C largest sum of magnitudes of real and imaginary parts. C ICAMAX = first I, I = 1 to N, to maximize C ABS(REAL(CX(IX+(I-1)*INCX))) + ABS(IMAG(CX(IX+(I-1)*INCX))), C where IX = 1 if INCX .GE. 0, else IX = 1+(1-N)*INCX. C C***REFERENCES C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T. C Krogh, Basic linear algebra subprograms for Fortran C usage, Algorithm No. 539, Transactions on Mathematical C Software 5, 3 (September 1979), pp. 308-323. C***ROUTINES CALLED (NONE) C***REVISION HISTORY (YYMMDD) C 791001 DATE WRITTEN C 861211 REVISION DATE from Version 3.2 C 891214 Prologue converted to Version 4.0 format. (BAB) C 900821 Modified to correct problem with a negative increment. C (WRB) C 920501 Reformatted the REFERENCES section. (WRB) C***END PROLOGUE ICAMAX COMPLEX CX(*) REAL SMAX, XMAG INTEGER I, INCX, IX, N COMPLEX ZDUM REAL CABS1 CABS1(ZDUM) = ABS(REAL(ZDUM)) + ABS(AIMAG(ZDUM)) C***FIRST EXECUTABLE STATEMENT ICAMAX ICAMAX = 0 IF (N .LE. 0) RETURN ICAMAX = 1 IF (N .EQ. 1) RETURN C IF (INCX .EQ. 1) GOTO 20 C C Code for increment not equal to 1. C IX = 1 IF (INCX .LT. 0) IX = (-N+1)*INCX + 1 SMAX = CABS1(CX(IX)) IX = IX + INCX DO 10 I = 2,N XMAG = CABS1(CX(IX)) IF (XMAG .GT. SMAX) THEN ICAMAX = I SMAX = XMAG ENDIF IX = IX + INCX 10 CONTINUE RETURN C C Code for increment equal to 1. C 20 SMAX = CABS1(CX(1)) DO 30 I = 2,N XMAG = CABS1(CX(I)) IF (XMAG .GT. SMAX) THEN ICAMAX = I SMAX = XMAG ENDIF 30 CONTINUE RETURN END