GPS-X Technical Reference

Optimizer 378
Time Series Optimization
This optimization type is the one normally used for both parameter estimation and
process optimization in GPS-X. It is designed to handle both time series and steady-state
measurements.
For this type of optimization, you enter your measured data into a text file with a .dat
extension. This text file should follow the naming and formatting conventions discussed
in the GPS-X User's Guide.
For parameter estimation involving a dynamic model, the data entered into the text file
will be a set of time series values for each of the response variables. In GPS-X the
response variables are referred to as target variables.
Steady-state optimization is a time series-type optimization with only one data point for
each target variable. The steady-state solver is used and the simulation has a stop time of
0.0. This type of optimization is useful for calibrating the model to data reported as daily,
weekly or monthly averages. Data of this type are typically obtained from composite
samples and thus do not accurately reflect the time dynamics of the real process. In a
steady-state optimization, the average data are used as the targets and selected model
parameters are adjusted to fit these targets.
When doing process optimization, you enter single target values for your process
performance measures at the desired points in time. As mentioned earlier, you should
also make sure to use the absolute difference objective function.
GPS-X will fit your model to the measured data using the objective function that you
select. If you prepare output graphs to display the predicted values of the model, GPS-X
will automatically display the measured values provided in the .dat file on the graphs.
GPS-X will draw a new curve for the predicted values at each optimization iteration, in
order to track the progress of the optimizer. At the end of the optimization process, final
predicted responses are displayed so that you can visually assess the fit. An example of
this type of graph is shown in Figure 14-3.
GPS-X Technical Reference