HP MLIB User's Guide Vol. 1 7th Ed.

50 HP MLIB User’s Guide
ISMAX/IDMAX/IIMAX Index of maximum element of vector
Use incx = 1 if the vector x is stored contiguously in
array x; that is, if x
i
is stored in x(i). Refer to “BLAS
Indexing Conventions” in the introduction to this
chapter.
Output i If n ≤ 0, then i = 0. Otherwise, i is the index of the
maximum element of x.
Fortran
Equivalent
INTEGER*4 FUNCTION ISMAX (N,X,INCX)
REAL*4 X(*),XMAX
ISMAX = 1
IF ( N .GT. 1 ) THEN
XMAX = X(1)
INCXA = ABS ( INCX )
IX = 1 + INCXA
DO 10 I = 2, N
IF ( X(IX) .GT. XMAX ) THEN
ISMAX = I
XMAX = X(IX)
END IF
IX = IX + INCXA
10 CONTINUE
ELSE IF ( N .LT. 1 ) THEN
ISMAX = 0
END IF
RETURN
END
Example Locate the largest element of a REAL*8 vector x, where x is a vector 10
elements long stored in a one-dimensional array X of dimension 20.
INTEGER*4 I,IDMAX,N,INCX
REAL*8 X(20)
N = 10
INCX = 1
I = IDMAX (N,X,INCX)