Running PEST

When you have set up the inputs and outputs in your model that will be used by PEST, you can go the the Actions tab in the PEST interface tool notebook and try to run it.

The run length from the run control will be used unless you alter it in the input box. If you do not select the checkbox in the Predictive analysis section, a simple parameter estimation will be done. Note that if all your outputs are time series, the run length will be up to the last time series value and the entry box for it will have no effect.

A PEST run can be controlled in the same way as a model run : it can start, stop or pause. The progress bar is inaccurate because it is impossible to tell in advance how many model runs PEST will need before it converges on the best parameters. It just shows what proportion has been done of the maximum number of runs specified in the settings.

While PEST is running you will see the run control values and progress bar update during each run. You will also see statistics about the run appear in the execution monitor box of the Actions tab. The text box in the execution monitor displays PEST's output to the command line, which is useful in case it should fail for any reason.

Simile's other helper tools are also updated while PEST runs. This means that if you have a slider tool for the variable parameters which are under PEST's control, you can watch them update as PEST adjusts them to optimize the outputs. However you may not want the tools to be updated, as they may slow down execution, and the plotter will show a separate trace for each run. To turn off all helper updates, set the 'Display interval' entry in the Run Control dialogue to zero. Alternatively you can set it to an interval longer than the run length, so the helpers (including sliders) will only be updated at the start of each run.

When PEST has finished optimizing, the model's parameters will be set to the values it has estimated. You can now go to the file parameters dialogue and save these  values in a scenario file if they will be required later. PEST provides an indication (the 'phi' value) of how good its estimation is, and this is reported in the Actio tab of the helper -- the lower the phi value, the better the estimation. For a graphical view, if you have a time series of measurements and you are displaying the corresponding model value on a tool such as the plotter, you can select the 'show these values on plots' checkbox at the bottom of the PEST tool Outputs panel, then reset and run the model again, and a trace of the measured data will be superposed on the model data trace in the plotter tool.

PEST produces a selection of output files during a run. These are kept in Simile's temporary directory. When PEST has finished running, you can save any of these in a permanent directory using the 'Save a PEST file...' button. Each pest file has a different extension; use the extension chooser in the save dialogue to choose the file you want, and enter the name you want to give it.

If PEST fails to converge on a good set of parameters, you can adjust its settings. The global settings, such as NOPTMAX to control the maximum allowed number of optimization stages, are on the Settings tab. Settings related to each input or output, such as PARCHGLIM which affects how the maximum change of an input value on a single step is applied, can be edited in a context menu for that input or output " right click (ctrl click on Mac) on the input or output field to bring this menu up. The labels on these entries correspond to the names of the settings as described in the PEST manual, which you should refer to when adjusting them.

In: Contents >> Running models >> PEST