# Random Number Generation

A sequence of random numbers is generated by specifying a "seed" value and entering this seed value into a "random number generator". For a given seed value and a given random number generator, the SAME sequence of random numbers will always be generated. A different seed, or a different generator, will produce a different sequence of random numbers.

The **Random Number Generation** is **Pseudo-Random**. **Pseudo-Random** analysis means that the analysis results will always be identical, each time the analysis is run. This is because the same "seed" is used in each case to generate the same sequence of random numbers, which is then used to generate the rockfall results.

**Random Number Generation** is configured in the **Random Number Generation** dialog through the **Project Settings Probability Settings** tab.

To open the tab:

- Open the
**Project Settings**dialog. - Select the
**Probability Settings**tab. - Click the
**Random Numbers**button. - Click
**Cancel**to close the dialog.

## Pseudo-Random Numbers

There are two options for the **Pseudo-Random Numbers** selection: **Default Seed** and **Custom Seed**.

### DEFAULT SEED

The purpose of the **Pseudo-Random Number** using the **Default Seed** value is to allow you to obtain reproducible analysis results, even though random numbers are used to generate some of the program input data. The **Default Seed** option is useful because, for the purposes of generating reports, presentations and demonstrations, it is often necessary to be able to present and discuss a known set of results.

By default, **RocFall** will always use the same "seed" value, to generate the same sequence of random numbers this value is hard-coded into the program. However, the user may also specify their own seed value, by selecting the **Custom Seed** option.

### CUSTOM SEED

The **Custom Seed** option allows you to specify your own seed value, rather than using the program's default seed value. To do this, select the **Custom Seed** check box, and enter any number.

The analysis will still be Pseudo-Random. That is, if you re-run the analysis, you will always get EXACTLY the same results. However, the results will NOT be the same as the results using the default seed value. In fact, each different value of seed will produce different results.

For any given constant seed value, you will always get the same results (i.e. endpoint graphs, distribution graphs, and all other analysis results).