anchor.diff:    solvent% force_old = solvent% force
     colloids% force_old = colloids% force
   
  -  write(*,*) ''
  -  write(*,*) '    i           |    e co so     |   e co co     |   kin co      |   kin so      |   total       |   temp        |'
  -  write(*,*) ''
  -
     kin_co = (mass(1)*sum(colloids% vel(:,1)**2)+mass(2)*sum(colloids% vel(:,2)**2))/2
  -  call thermo_write
  -
  +
  +  write(*,*) 'Running for', N_loop, 'loops'
     call main%tic()
     do i = 1, N_loop
  +     if (modulo(i,5) == 0) write(*,'(i05)',advance='no') i
        md_loop: do j = 1, N_MD_steps
           call md_pos(solvent, dt)
   
  
positive.code: 
    mass(1) = rho * sigma_C**3 * 4 * 3.14159265/3
    mass(2) = rho * sigma_N**3 * 4 * 3.14159265/3
    write(*,*) 'mass =', mass
  
    call solvent% init(N,2) !there will be 2 species of solvent particles
  
  
negative.code: 
    end do
    call main%tac()
    write(*,*) ''
  
    write(*,*) 'n extra sorting', n_extra_sorting
    
  