Index of Element with Maximum Absolute Value

which is the l-norm of a vector x.

IZAMAX and ICAMAX return the smallest index i where

Note that this does not return an index i such that

which is the l-norm for a complex vector.

Note also that the FORTRAN interfaces return an index based at one while the C interfaces return an index based at zero. This is in keeping with the convention of each language in which the first element of a FORTRAN array is usually 1 and the first element of a C array is 0.

Calling Sequence

I = IDAMAX (N, DX, INCX)

I = ISAMAX (N, SX, INCX)

I = IZAMAX (N, ZX, INCX)

I = ICAMAX (N, CX, INCX)

int idamax (int n, double *dx, int incx)

int isamax (int n, float *sx, int incx)

int izamax (int n, doublecomplex *zx, int incx)

int icamax (int n, complex *cx, int incx)

Arguments

N	Number of elements in the vector. N 0.
xX	Input vector X; the size of array X must be at least max(1,N*|INCX|).
INCX	Specifies the storage spacing between successive elements of the vector X. A value of one indicates that the elements of the vector are consecutive in memory. INCX > 0.
	If X refers to a two-dimensional array and the value of INCX is equal to the leading dimension of X then the elements of the vector will be a row of X.
	If X refers to a two-dimensional array and the value of INCX is equal to the leading dimension of X plus one then the elements of the vector will be a diagonal of X.

Sample Program

PROGRAM TEST

IMPLICIT NONE

C

INTEGER N

PARAMETER (N = 5)

C

COMPLEX X(N)

INTEGER I, ILARGE, INCX

C

INTEGER ICAMAX

EXTERNAL ICAMAX

C

C Initialize the array X to store the vector x shown below.

C

C 5-4i

C -3-2i

C x = 5-4i

C 6+0i

C 0+8i

C

DATA X / (5.0,-4.0), (-3.0,-2.0), (5.0,-4.0), (6.0,0.0),

$ (0.0,8.0) /

C

INCX = 1

ILARGE = ICAMAX (N, X, INCX)

PRINT 1000

PRINT 1010, (X(I), I = 1, N)

PRINT 1020, ILARGE

C

1000 FORMAT (1X, 'x:')

1010 FORMAT (3X, '(', F4.1, ',', F4.1, ')')

1020 FORMAT (/1X, 'Largest element in the vector x is item ', I1)

C

END

Sample Output

x:
( 5.0,-4.0)
(-3.0,-2.0)
( 5.0,-4.0)
( 6.0, 0.0)
( 0.0, 8.0)
Largest element in the vector x is item 1