Frequently Asked Questions

This manual gives answers that have been frequently asked by XSIM users. Unless otherwise stated, references are to sections of the Interface Reference Manual.

Q. What environment variables are used by XSIM?

A. The environment variables used by XSIM are described in section 2.1.

Q. What mouse buttons are used by XSIM?

A. The left and right mouse buttons have special uses in XSIM. These are described in section 2.4.

Q. How do I change the increment and maximum value of the independent variable for a simulation run?

A. The starting value, increment, and final values of the independent variable are set in the independent variable window which is accessible through the Parameters menu (section 8.5.2).

Q. I have set X maximum to 30 seconds in a plot area; why does the model keeps running after the solution has reached 30 seconds?

A. A simulation run normally terminates when the independent variable reaches the stopping value set in the independent variable window (section 8.5.2). The value of X maximum in a plot window only controls the plotting and does not affect the stopping value for the independent variable.

Q. How can I print an XSIM plot?

A. To print a plot select the print option in the results menu. In the window that pops up, select the graph option for plot area 1 and/or 2 as appropriate and click the print button. More details about printing are given in section 8.6.11.

Q. Since the labels used for parameters are sometimes different than their actual names, how do I find the name of a parameter to enter it into a field such as a plot Y-parameter or parameter to be optimized?

A. You can find the name of a parameter by opening a window that contains the parameter, and clicking on the parameter value field. The parameter name will be displayed in the paste area of the XSIM main window. (You may need to enlarge the window to see the complete name.) The paste area is described in section 2.5. You can often use the paste button to paste this name into the currently selected field. You can also get lists of parameter names by using the right mouse button to open a pick control window. More details are given in section 2.5.3 (Pick control windows).

Q. What causes some simulations to run so much slower than others even when the model is unchanged?

A. There can be several causes that may be beyond your control such as the computational load on your computer from other tasks running simultaneously. Two things that you can control are the number of XSIM windows that are being updated during the run and frequent rescaling of plot windows due to autoscaling. It takes time to update text fields. Iconifying windows with many text fields during a run can speed the run significantly. Similarly, redrawing a plot that rescales frequently takes time. Try using manual scaling on the Y-axis and autoscale the plot at the end of the run if necessary.

Q. What does filter mean in the file selection window opened when I want to load a parameter or reference data file?

A. The filter controls the files shown in the files list. It can contain the same wildcard characters as those used by your command shell. More details are given in section 2.5.3 (File selection windows).

Q. What mathematical operators can I use when I enter a parameter expression in a text field?

A. You can use arithmetic operators and many common mathematical operators. A complete list is given in The XSIM Expression Evaluator appendix.

Q. What is the meaning of an @ in a parameter expression?

A. The @ symbol is an abbreviation for that can be used for a parameter name in a loop expression (section 8.2.3) or reference data in a point weight expression (section 8.2.4, Reference Curves to Match).

Q. XSIM crashes when I run my model, and the message ``realloc error'' is displayed in my terminal window. What's wrong?

A. The amount of memory required to store the model results exceeds that currently available. One option is to increase available memory by exiting from other programs, but in a multi-user environment, this may not be practical. A second option is to reduce the amount of memory required by XSIM to store results. This can be done by selecting options in the Save Results section of the Run config window (found in the Model menu). These options are described in section 8.2.3.

Copyright 1995-1998, University of Washington

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