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Section Arrays: Submatrices¶

Adapted from: https://github.com/gjbex/Fortran-MOOC/tree/master/source_code/arrays

This program demonstrates matrix slicing in Fortran.¶

program submatrices
  implicit none
  integer, dimension(3, 4) :: A
  integer, dimension(12)   :: A_array
  integer :: i, j

  A_array = [ (((i - 1)*size(A, 2) + j, &
                   j=1, size(A, 2)), &
                   i=1, size(A, 1)) ]

  A = reshape([ (((i - 1)*size(A, 2) + j, &
                   j=1, size(A, 2)), &
                   i=1, size(A, 1)) ], &
              shape(A))
              
  
  print *, "A_array contains: ", A_array

  print *, "A matrix contains: "
  
  do i = 1, size(A, 1)
    print *, A(i, :)
  end do

  print *
  print *, "Row 2 contains: "
  print *, A(2, :)
  print *, "Column 3 contains: "
  print *, A(:, 3)
  print '(A, I0)', 'rank = ', rank(A(2, :))
  print '(A, I0)', 'shape = ', shape(A(2, :))
end program submatrices

The above program is compiled and run using Fortran Package Manager (fpm):

Build the Program using FPM (Fortran Package Manager)¶

import os
root_dir = os.getcwd()

code_dir = root_dir + "/" + "Fortran_Code/Section_Arrays_Submatrices"

os.chdir(code_dir)

build_status = os.system("fpm build 2>/dev/null")

Run the Program using FPM (Fortran Package Manager)¶

exec_status = os.system("fpm run 2>/dev/null")

 A_array contains:            1           2           3           4           5           6           7           8           9          10          11          12
 A matrix contains: 
           1           4           7          10
           2           5           8          11
           3           6           9          12

 Row 2 contains: 
           2           5           8          11
 Column 3 contains: 
           7           8           9
rank = 1
shape = 4