Fixed the verlet method. Created matrices that saves the position and velocity of all objects at the same time in order to compute the time steps and position correctly (positions of all objects need to be calculated at the same time in order to avoid a displacement in the force calculations). Added a routine which saves the positions of all objects to a file Data_RK4.dat or Data_verlet.dat in order to plot the positions. Fixed the force calculations (counted each planet twice). IT WORKS *exclamation mark*