5.1.6 Generating models

Besides a variety of programs of the kind of mkplummer, mkommod, mkexpdisk etc., models can also be generated by calculating appropriate tables (containing a run of density, potential and radius) and feeding them into programs which translate such tables into a snapshot. An example of a program in the making is anisot.

An alternative way is to use a package such as Mathematica to integrate the differential equations. With the following example we leave this as an exercise to the reader:

  << NumericalMath/RungeKutta.m

  rpsipsiprime = RungeKutta[{psiprime, -(2/r)psiprime + Exp[-psi]},
    {r, psi, psiprime}, {10^-5, 10^-10/6, 10^-5/3}, 50, 10^-8,
    MaximumStepSize->0.5];

  rpsi = rpsipsiprime[[Table[n,{n,Length[rpsipsiprime]}],{1,2}]];

  r = rpsi[[Table[n,{n,Length[rpsi]}],1]];

  psi = rpsi[[Table[n,{n,Length[rpsi]}],2]];

  rho = Exp[-psi];

  rrhotranspose={r,rho};
 
  rrho = Transpose[rrhotranspose];

  logrlogrho = Map[Log, rrho, {2}];

  c = Log[10.];

  log10rlog10rho = logrlogrho / c;

  shortrrho = Take[rrho,30];

  PlotODESolution[shortrrho, 1, 2, 
        AxesLabel-> {"r", "rho"}, 
        PlotLabel -> "Isothermal Sphere"]

  PlotODESolution[log10rlog10rho, 1, 2, 
        AxesLabel-> {"log r", "log rho"}]