Finds the index of the element with maximum absolute value.

Syntax

index = isamax(n, x, incx)

index = idamax(n, x, incx)

index = icamax(n, x, incx)

index = izamax(n, x, incx)

index = iamax(x)

Include Files

  • mkl.fi, blas.f90

Description

Given a vector x, the i?amax functions return the position of the vector element x(i) that has the largest absolute value for real flavors, or the largest sum |Re(x[i])|+|Im(x[i])| for complex flavors.

If either n or incx are not positive, the routine returns 0.

If more than one vector element is found with the same largest absolute value, the index of the first one encountered is returned.

If the vector contains NaN values, then the routine returns the index of the first NaN.

Input Parameters

n

INTEGER. Specifies the number of elements in vector x.

x

REAL for isamax

DOUBLE PRECISION for idamax

COMPLEX for icamax

DOUBLE COMPLEX for izamax

Array, size at least (1+(n-1)*abs(incx)).

incx

INTEGER. Specifies the increment for the elements of x.

Output Parameters

index

INTEGER. Contains the position of vector element that has the largest absolute value such that x(index) has the largest absolute value.

BLAS 95 Interface Notes

Functions and routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or reconstructible arguments, see BLAS 95 Interface Conventions.

Specific details for the function iamax interface are the following:

x

Holds the vector with the number of elements n.

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