.LP
Xprism2 has a built-in function parser that can be used to generate 
2D data points from a function automatically.  Fill in the function, the X 
minimum and maximum points, and the total number of X points. 
All functions are entered in cartesian coordinates.
An example of a 2D function is 3*cos(x).  Note
that when entering a 2D function, the ONLY accepted variable is "x".  Attempting
to use any variable other than "x" will cause an error message.  
.LP
When providing a function to xprism2, one must make sure that the maximum and 
minimum X points (the bounds of the plot), are specified correctly in the
parameters labeled "X Minimum", "X Maximum" and "Number of Points", 
respectively.  The defaults are -1 to 1 with a total of 30 points. Be sure
that the function is defined over the interval specified.  If the function 
provided is not defined vier the given interval, 2 things may occur:  
.IP (1)
The built-in parser will generate an error message 
.IP (2)
Round-off error may cause the parser to compute points that are
NOT EXACTLY at the point where the function is UNDEFINED.  In this case, xprism2
will go ahead and plot the function to the best of its ability, in spite of the
fact that it is undefined over the specified interval.  Results may or may not
be close to the correct graph of the function.
.IP (3)
If there is an error that the signal handlers in Xprism2 cannot handle, the
package will core dump.
.LP
The function "minimun", "maximum", and "number of points" fields are
string fields. Therefore, for any of these fields a constant such as "pi", 
or an expression such as tan(0.9923) can be entered. The only restriction
is that the expression can not be a function of x or y.
.LP
To plot the 2D function, make sure that all parameters are filled out correctly,
and click on the "PLOT FUNCTION" action button.  The function will be evaluated
as indicated and displayed accroding to the current value of the "plot type"
toggle.
.SH
Points to Be Displayed
.IP 
The option labeled "Points to be Displayed" allows the user to window on 
a specified portion of the data. In addition to windowing, the user may also 
subsample the data to be displayed. All data is read in when
the "Plot File" button is clicked with the mouse; the "Points to be Displayed"
option works on that data. Once plotted, the window and subsampling parameters 
may be changed for each currently displayed plot using the "Attributes" 
subform. The "Points to be Displayed" option has three items that can be 
changed. The following explains these options:
.RS
.IP "Step Size"
This "Step Size" option specifies how the data should be subsampled
between the begin point and the end point. The default value is 1; ie, every
point is used.
.IP "Begin Point"
The "Begin Point" specifies the first of the data points to plot. That is,
which data point to begin with, the data points being numbered sequentially. 
For example, if the "Begin Point" is specified as 5, the plot will start with
the fifth data point.  If the "Begin Point" is set to 0 (the default value), 
then the "end point" is ignored and all data points are used.
.IP "End Point"
The "End Point" specifies the last of the data points to plot. That is,
which data point to end with, the data points being numbered sequentially.
For example, if the "End Point" is specified as 25, the plot will end with the
twenty-fifth data point. If the "End Point" is set to 0 (the default value), 
then the last data point in the file is used as the end point.
.RE
.SH
Plot Type
.IP 
Each plot that is input will be displayed as the plot type that is indicated
by the "plot type" toggle in the "Input File" pane.  Thus, by changing
the plot type before each new plot is displayed, any of the five plot types
may be displayed simultaneously in the graphics workspace.
