XSIM is a graphical user interface for use by biomedical investigators doing computer simulation. XSIM runs in a windowing environment on engineering workstations and uses the ``point and click'' approach that has become popular with modern computer users. An important feature of XSIM is that the appearance of the screen is not predefined but is determined at run time by reading a configuration file selected by the investigator. The content and appearance of pop-up windows related to the model and its parameters are specified in the configuration file. This allows the interface to be tailored to the specific analysis task at hand including a graphical depiction of the model being run.

Since the interface and model run as separate tasks, the investigator can shift to different models without leaving the interface. Other capabilities include parameter optimizers to fit model output to experimental data, analysis of sensitivity and residual functions, graphical display of data, and an expression parser that enables the investigator to define new variables at run time. The first implementation of XSIM is on Sun SPARC stations using Motif, but its design facilitates portability to other hardware platforms and window systems.

While there are several ways to load and run a model under XSIM, only one is described here. After the XSIM program is started, the user selects the model select option from the model menu, enters a name into the text field in the dialogue box, and clicks the load button. XSIM reads the configuration file, loads the model program and entries for the parameters menu, pops up windows specified by the configuration file, and displays the ``ready for user input'' message in the diagnostic window. The user can now click the run button and start a simulation run.

The user can display the results by selecting options from the results menu and can change the values of model parameters, including those for controlling the independent variable, by selecting options in the parameters menu.

With a model loaded, the user can examine the sensitivity of model solutions to the model parameters by completing the entries required in the sensitivity configuration dialogue box accessed under the model menu, clicking the sensitivity button, and displaying the results.

The model parameters and configuration of the XSIM interface can be saved in a file by selecting the save or save as option from the par-file menu. These parameter files can be reloaded using XSIM.

Data can be analyzed by fitting the model output(s) to experimental (reference) data by manually adjusting the model parameters or by using one of two optimizers to automatically adjust model parameters to obtain the best fit of the model to the data.

In either case, the user loads the reference data by selecting the select TAC file option from the reference menu. (TAC stands for Time Activity Curve.) If an optimizer is to be used, the user must complete the information required in the optimization configuration dialogue box accessed under the model menu.

The user can check the fit of the model to the data by clicking the residuals button and displaying the residuals graph and/or report using the results menu.

To exit XSIM the user selects the quit option from the model menu. If the parameters are different than the last time they were saved, XSIM will prompt the user to save their values.

On-line help is available through the help menu. The user can get context-sensitive help by selecting the on context option (or using the F1 key) or can view documents from the XSIM documentation package.

Items in the help menu also give users who are connected to the World Wide Web access to XSIM updates and bug reports. For the latter, the user can file a new report or view outstanding reports.

Copyright 1995-1998, University of Washington

Last modified: 12:58pm PDT October 17, 1998