anchor.diff:  
      call dgemm('n', 'n', n, n, n, 1.0d0, a, n, b, n, 0.0d0, c, n)
   
  +   test_ok = .true.
  +
      do i = 1, n
         do j = 1, n
  -         if (dabs(c(i, j) - 20.0d0) > tiny(0.0d0)) return
  +         if (dabs(c(i, j) - 20.0d0) > tiny(0.0d0)) then
  +            print *, 'ERROR: element', i, j, 'is', c(i, j)
  +            test_ok = .false.
  +         end if
         end do
      end do
   
  
positive.code:    deallocate(b)
     deallocate(c)
  
     print *, 'dgemm test ok'
  
  end program
  
negative.code:    integer, parameter :: n = 10
  
     integer :: i, j
     logical :: test_ok
  
     real(8), allocatable :: a(:, :)
     real(8), allocatable :: b(:, :)
  