'draw.gamma' computes the X-Y coordinates for a gamma probability density function if 'cdf = FALSE' or the X-Y coordinates of the gamma cumulative distribution function if 'cdf = TRUE'.  It either plots the function or simply outputs the coordinates.

ARGUMENTS: 

'shape' = shape parameter of the gamma

'rate' = rate parameter of the gamma.  Note that you only need to specify the 'rate' or the 'scale' but not both.  If both are specified, then the 'scale' parameter takes precedence.

'scale' = scale parameter.  See comment about the 'rate' parameter.

'xlimit = NA' permits user control of the x axis limits.

'ylimit = NA' permits user control of the y axis limits.

'plot.dist = T':  If FALSE, then no plot is made and the X-Y coordinates for the graph are outputted.  If TRUE, a plot is made and the coordinates are not outputted.

'cdf':  If 'cdf = TRUE', then the cumulative distribution function is plotted (if a plot is requested) or the X-Y cooredinates for the plot are outputted.  If 'cdf = FALSE' (default), then the density function is plotted (if a plot is requested) or the X-Y cooredinates for the plot are outputted.

'Label = "default"':  The default setting creates a graph title that states the parameters of the gamma distribution.  If 'Label' is not set to "default", then no axis labels or graph title are created.  The user can add these labels after creating an initial graph of the gamma distribution.  

'Lwd' controls the line weight on the graph.

'cred.int' & 'plot.cred.int' control whether or not a credible interval is plotted and the probability level of the credible interval.  At present, only a two-sided credible interval is implemented, but in the future, I would like to offer the option of plotting the credible interval in the left or right tail of the distribution.  

'cred.lab' controls whether or not the probability level of the credible interval is plotted inside of the density plot.

'cred.col' controls the color of the area under the credible interval.

'plot.stats = TRUE' (default): mean, sd & quantiles are plotted on the figure.

If 'x.stats.coord = NA', then the function chooses an X coordinate for plotting stats.  If the user specifies a value for 'x.stats.coord', then that value overrides the default choice of X coordinate.