Does MINLOC work for arrays beginning at index 0? (Fortran 90/95)

Question

After using C for a while, I went back to Fortran and allocated the arrays in my code from index 0 to N:

real(kind=dp), dimension(:), allocatable :: a 
alloc         


        

Answer 1

There are two simple methods to handle complication of adjusting the indices obtained from minloc(): One is simply adding lbound() - 1 for all indices, and the other is using an array pointer with 1-based indices. An example code may look like this:

program test
implicit none
integer, allocatable, target :: a(:,:)
integer, pointer :: anew(:,:)
integer :: loc(2)

allocate( a( 0:4, 2:5 ), source= 10 )  !! make an array filled with 10

a( 2, 3 ) = -700                       !! set the minimum value

loc(:) = minloc( a )                   !! minloc() receives "a" with 1-based indices
print *, loc(:)                        !! so we get [3,2]
print *, a( loc(1), loc(2) )           !! 10 (wrong result...)

!! Method (1) : adjust indices manually

loc(:) = loc(:) + lbound( a ) - 1
print *, a( loc(1), loc(2) )           !! -700 (now a correct result)

!! Method (2) : use array pointer with 1-based indices

anew( 1:, 1: ) => a

loc(:) = minloc( anew )
print *, loc(:)                        !! we get [3,2] again
print *, anew( loc(1), loc(2) )        !! -700  (this time, no need to adjust indices)

end program