Running models : Working with visualisation tools : Initialise

Standard helpers: Initial pseudo-random number generator

The functions rand_var() and rand_const() generate random numbers. For greater understanding of model behaviour it is sometimes convenient to generate the same (or the same sequence) of random numbers for several model runs. To do this, it is necessary to seed the random number generator with the same integer value each run. For this reason, they are known as pseudo-random numbers. A simple tool is provided to enter the seed.

To enter the seed:

  1. enter an integer value in the edit box;
  2. click on the "Set seed" button; and
  3. reset the model.

Note: It is important that the reset button on the "Run Control" is used AFTER initialising the pseudo-random number generator using the "Set seed" command. This is because some random numbers are generated when the model is reset.


Using the seed "123" will produce the following sequence of random numbers for the function rand_var(0,100) every time the simulation is performed:

62.3463, 2.2889, 13.6723, 11.7893, 92.8648, 56.7217, 93.8688, 96.4232, 96.3378, 75.1671, 49.0097, …

(At least if you are using the bundled MinGW C compiler under Windows. Other compilers may produce different sequences, owing to using different library implementations of the pseudorandom sequence generators, but this tool can still be used to achieve repeatability.)

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