# Dimerisation

The dimerisation process has two species P and P2 with initial amounts of 100 and 0, respectively. There are two reactions which both have mass-action kinetics: 2P → P2 and P2 → 2P and two reactions

## dsmts-002-01

The immigration and death reactions have mass-action kinetic laws with rate parameters Alpha = 1 and Mu = 0.1, respectively. Use `File→Import SBML` to import the file `examples/sbml/dsmts31/dsmts-001-01.xml`. The model is imported correctly, however the reactions are not recognized as having mass-action kinetics. Edit the reactions to reflect this. Add a method in the methods list. In the methods editor select `Time Homogeneous` and `Time Series, Uniform` with the default solver and options. Set the recording time to 50 and the number of frames to 51. To see the result of these modifications open the file `examples/cain/dsmts31/dsmts-002-01.xml`. Below is the plot of the mean and standard deviation of the species population calculated from 10,000 trajectories. (We have set the lower bound on the Y axis to 0 in the plot configuration window.)

Note that this problem has a steady state solution. Select `SteadyState` in the methods list panel. In calculating the steady state solution, we let the process equilibrate for 100 time units and then record the state for 100,000 time units. We generate four trajectories and plot the steady state histogram, shown below.

With the steady state output selected, click the table button and then select `Estimated Error`. The estimated error in the probability distribution is 0.0045.