anchor.diff:    call GET_COMMAND_ARGUMENT(3, str_solver_choice)
     read(str_solver_choice, '(I50)') which_solver
     if ( .not. ( which_solver == 1 .or. which_solver == 2 )) then
  -     write(*,*) 'ERROR: which_solver should be 1 or 2.'
  -     stop
  +     invalid_arguments = .true.
     end if
     if ( which_solver == 1 ) then
        write(*,*) 'Using Nonzero Gauss-Jordan Solver'
  
positive.code:   call GET_COMMAND_ARGUMENT(4, str_iters_choice)
    read(str_iters_choice, '(I50)') which_iters
    if ( .not. ( which_iters == 1 .or. which_iters == 2 )) then
       write(*,*) 'ERROR: which_iters should be 1 or 2.'
       stop
    end if
  
  
negative.code:      write(*,*) 'NO SOLVER SPECIFIED. ENTER 1 or 2.'
       stop
    end if
    aresid = abs(xtrue - xsolv)
  end subroutine random_solve
  
  program test_gj_solve
    ! Takes 4 command-line arguments:
    ! 1: Name of sparsity structure file to read
    ! 2: Number of random matrix equations Ax=b to solve
    ! 3: Which solver to use (1 = gauss jordan, 2 = LAPACK DGESV)
    ! 4: Matrix generation (1 = resample matrix every iteration,
    !                       2 = randomly sample matrix only once)
    
    implicit none
    
  