Particle oscillation on a spring

turtles-own 
[delta_V_y delta_y delta_t d_y]

globals
[l m k F V_y E_k E_p E_uk a]

to setup
  clear-all
  setup-opruga
  setup-čestica
  reset-ticks
end 

to setup-opruga
  ask patches
  [
    set pcolor white
  ]
  ask patch 0 1 [set pcolor yellow]
  ask patch -1 1 [set pcolor yellow]
  ask patch -2 1 [set pcolor yellow]
  ask patch 1 1 [set pcolor yellow]
  ask patch 2 1 [set pcolor yellow]
  set l length_of_the_spring 
  ask patch 0 (0 - l) [set pcolor red]
end 

to setup-čestica
  create-turtles 1
  ask turtle 0 
    [
    setxy 0 random (0 - l) * 2
    set color green
    set shape "circle" 
    ]   
end 

to go
  ask turtle 0 
  [
  unos
  izračun
  ]
  tick
end 

to unos
  set delta_t 0.001
  set k constant_of_the_spring
  set m mass_of_the_particle
end 

to izračun 
  set delta_y (abs ycor) - l
  set F (k * delta_y) 
  set delta_V_y (F * delta_t) / m
  set V_y (V_y + delta_V_y)
  set d_y (V_y * delta_t)
  set ycor (ycor + d_y)
  set E_k (m * V_y * V_y) / 2
  set E_p (k * delta_y * delta_y) / 2
  set E_uk E_k + E_p
  set a delta_V_y / delta_t
end