Language Reference

MAXLOC(ARRAY, DIM, MASK) or MAXLOC(ARRAY, MASK)

Locates the first element of an array along a dimension that has the maximum value of all elements corresponding to the true values of the mask. MAXLOC will return the index referable to the position of the element using a positive integer.

ARRAY

is an array of type integer or real.

+---------------------------------Fortran 95---------------------------------+

DIM (optional)

is a scalar integer in the range 1<=DIM<=rank(ARRAY).

+-----------------------------End of Fortran 95------------------------------+

MASK (optional)

is of type logical and conforms to ARRAY in shape. If it is absent, the default mask evaluation is .TRUE.; that is, the entire array is evaluated.

Class

Transformational function

Result Type and Attributes

If DIM is absent, the result is an integer array of rank one with a size equal to the rank of ARRAY. If DIM is present, the result is an integer array of rank rank(ARRAY)-1, and the shape is (s₁, ..., s_DIM-1, s_DIM+1, ..., s_n), where n is the rank of ARRAY.

If there is no maximum value, perhaps because the array is zero-sized or the mask array has all .FALSE. values or there is no DIM argument, the return value is a zero-sized one-dimensional entity. If DIM is present, the result shape depends on the rank of ARRAY.

Result Value

The result indicates the subscript of the location of the maximum masked element of ARRAY. If more than one element is equal to this maximum value, the function finds the location of the first (in array element order). If DIM is specified, the result indicates the location of the maximum masked element along each vector of the dimension.

+---------------------------------Fortran 95---------------------------------+

Because both DIM and MASK are optional, various combinations of arguments are possible. When the -qintlog option is specified with two arguments, the second argument refers to one of the following:

• MASK if it is an array of type integer, logical, byte or typeless
• DIM if it is a scalar of type integer, byte or typeless
• MASK if it is a scalar of type logical

The addition of the DIM argument modifies the behavior from XL Fortran Version 3.

+-----------------------------End of Fortran 95------------------------------+

Examples

! A is the array  |  4  9  8 -8 |
!                 |  2  1 -1  5 |
!                 |  9  4 -1  9 |
!                 | -7  5  7 -3 |
 
! Where is the largest element of A?
       RES = MAXLOC(A)
! The result is | 3 1 | because 9 is located at A(3,1).
! Although there are other 9s, A(3,1) is the first in
! column-major order.
 
! Where is the largest element in each column of A
! that is less than 7?
       RES = MAXLOC(A, DIM = 1, MASK = A .LT. 7)
! The result is | 1 4 2 2 | because these are the corresponding
! row locations of the largest value in each column
! that are less than 7 (the values being 4,5,-1,5).

Regardless of the defined upper and lower bounds of the array, MAXLOC will determine the lower bound index as '1'. Both MAXLOC and MINLOC index using positive integers. To find the actual index:

       INTEGER B(-100:100)
! Maxloc views the bounds as (1:201)
! If the largest element is located at index '-49'
       I = MAXLOC(B)
! Will return the index '52'
! To return the exact index for the largest element, insert:
       INDEX = LBOUND(B) - 1 + I
! Which is:  INDEX = (-100) - 1 + 52 = (-49)
       PRINT*, B(INDEX)