The N-body code, NBODY1, is initialized by input of mass, position, and velocity in physical coordinates, which are outputs from the AVP code. These initial values are given at time a=0.01, i.e. redshift 1+z=100, and the N-body code calculates the orbits forward in time until the current epoch .
The N-body solution of the galaxy system in Subsection 5.1.2, is presented in Figure 5.2, together with the solution from the AVP. The N-body solution is represented as dotted lines, while the respective AVP solution is given as solid lines. The difference between the action and the N-body orbits is a result of limited accuracy in the computation of the stationary value of the action, especially due to the truncation of the orbits in equation (3.21). However, the difference between the N-body and action orbits are small, indicating that the action solution is a useful approximation to the true orbits.
The N-body code will henceforth only be used to test the validity of the action solutions, discarding the ones that fail the test. The N-body solutions will not be presented in any other maps in this thesis--all the accepted solutions have similarly good agreement between the N-body and AVP orbits as in Figure 5.2.