d0/da5/izamax_8f_source.html

00001       INTEGER FUNCTION IZAMAX(N,ZX,INCX)
00002 *     .. Scalar Arguments ..
00003       INTEGER INCX,N
00004 *     ..
00005 *     .. Array Arguments ..
00006       DOUBLE COMPLEX ZX(*)
00007 *     ..
00008 *
00009 *  Purpose
00010 *  =======
00011 *
00012 *     IZAMAX finds the index of element having max. absolute value.
00013 *
00014 *  Further Details
00015 *  ===============
00016 *
00017 *     jack dongarra, 1/15/85.
00018 *     modified 3/93 to return if incx .le. 0.
00019 *     modified 12/3/93, array(1) declarations changed to array(*)
00020 *
00021 *  =====================================================================
00022 *
00023 *     .. Local Scalars ..
00024       DOUBLE PRECISION DMAX
00025       INTEGER I,IX
00026 *     ..
00027 *     .. External Functions ..
00028       DOUBLE PRECISION DCABS1
00029       EXTERNAL DCABS1
00030 *     ..
00031       IZAMAX = 0
00032       IF (N.LT.1 .OR. INCX.LE.0) RETURN
00033       IZAMAX = 1
00034       IF (N.EQ.1) RETURN
00035       IF (INCX.EQ.1) THEN
00036 *
00037 *        code for increment equal to 1
00038 *
00039          DMAX = DCABS1(ZX(1))
00040          DO I = 2,N
00041             IF (DCABS1(ZX(I)).GT.DMAX) THEN
00042                IZAMAX = I
00043                DMAX = DCABS1(ZX(I))
00044             END IF
00045          END DO
00046       ELSE
00047 *
00048 *        code for increment not equal to 1
00049 *
00050          IX = 1
00051          DMAX = DCABS1(ZX(1))
00052          IX = IX + INCX
00053          DO I = 2,N
00054             IF (DCABS1(ZX(IX)).GT.DMAX) THEN
00055                IZAMAX = I
00056                DMAX = DCABS1(ZX(IX))
00057             END IF
00058             IX = IX + INCX
00059          END DO
00060       END IF
00061       RETURN
00062       END