[ACCEPTED]-Implicit do loop array initialization-fortran

Accepted answer

Score: 22

You are initializing an array with MAXDIM rows 17 and NR columns, and it looks like each column 16 contains the integers 1 to MAXDIM.

As a first step, go 15 ahead and write out the actual DO-loop:

do j=1,NR
    do i=1,MAXDIM
        myarray(i,j) = i
    end do
end do

Collapse 14 the inner loop to an implicit loop structure:

do j = 1,NR
    myarray(1:MAXDIM,j) = (/ (i, i=1,MAXDIM) /)
end do

When 13 we try to collapse the outer loop, though, something 12 strange happens:

myarray = (/ ((/ (i, i=1,MAXDIM) /), j=1,NR) /)

Now, I get an incompatible 11 ranks error as you did. Since I'm not very 10 good at the implicit do-loops either, I 9 looked at the shape intrinsic results for the 8 array constructor:

print *, shape(myarray)
print *, shape((/ ((/ (i, i=1,MAXDIM) /), j=1,NR) /))

This prints out

   5      10
  50

The array 7 constructor is simply expanding a 1-D array 6 , flattening any nested array constructions. We 5 can actually drop the second set of (/ /) to 4 simplify. Since everything is already in 3 the proper order, we can use the reshape intrinsic 2 to ensure proper rank. My full test program 1 is then:

program sotest
    implicit none

    integer, parameter :: MAXDIM = 5
    integer, parameter :: NR     = 10

    integer :: i
    integer :: j
    integer :: myarray(MAXDIM, NR)
    integer :: myarray_implicit(MAXDIM, NR)

    do j = 1,NR
        do i = 1,MAXDIM
            myarray(i,j) = i
        end do
    end do 

    myarray_implicit = reshape((/ ((i,i=1,MAXDIM), j=1,NR) /), (/ MAXDIM, NR /))

    print *, all(myarray == myarray_implicit)
 end program sotest

Score: 7

The implicit do loop will only create a 6 vector so you'll have to reshape that. Something 5 like this:

integer, dimension(m,n) :: myarray
integer :: ix, jx
...
myarray = reshape( [ (ix, ix = 1, m*n) ], [ m, n ] )

or perhaps you want a more complicated, nested, implied-do 4 loop:

myarray = reshape( [ ((ix+jx, ix = 1, m), jx = 1, n) ], [ m, n ] )

Note that I'm using the Fortran2003 3 convention of [ ] to delimit array constructions, rather 2 than (/ /). Note also that you have to declare 1 the implied do loop index variables.

Source: stackoverflow.com

[ACCEPTED]-Implicit do loop array initialization-fortran

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