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# Varying parameters in a simulation

Nothing should remain constant in a dynamic model. In this respect, Dinamica EGO enables to vary model parameters either in different simulation phases or at each time step. In the Stack tab, a set of Select Functors can be used to change the values of input parameters according to the model step.

**Using different transition matrices**

For examples, instead of using only a constant transition matrix, Select Transition Matrix enables the use of different transition matrices in a simulation.

To start, load the model “simulate_deforestation_using_multiple_transition_matrix.xml” from \ advanced\multiple_parameters\simulate_deforestation_using_multiple_transition_matrix

Using more than one transition matrix in a model is quite simple. In this version of a deforestation model, *Select Transition Matrix* was added to allow the choice of a transition matrix according to the model step. Each transition matrix is entered in a Number Transition Matrix, click on this functor with the Edit Functor.

**Matrix Number** in this functor indentifies the model step in which this transition matrix begins to operate. The model will use this matrix until it finds a *Number Transition Matrix* with **Matrix Number** that corresponds to the current model step, while from this point onwards Select Transition Matrix switches to the new transition matrix.

**TIP**: you can use as many transition matrices as time steps. You just need to add more

*Number Transition Matrix*functors and number them according to the model time intervals.