(ddd.info)Scalars and Composites

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7.4.3 Plotting Scalars and Composites
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Besides plotting arrays, DDD also allows you to plot scalars (simple
numerical values).  This works just like plotting arrays--you select
the numerical variable, click on `Plot', and here comes the plot.
However, plotting a scalar is not very exciting.  A plot that contains
nothing but a scalar simply draws the scalar's value as a Y
constant--that is, a horizontal line.

   So why care about scalars at all?  DDD allows you to combine
_multiple values into one plot._  The basic idea is: if you want to
plot something that is neither an array nor a scalar, DDD takes all
numerical sub-values it can find and plots them all together in one
window.  For instance, you can plot all local variables by selecting
`Data => Display Local Variables', followed by `Plot'.  This will
create a plot containing all numerical values as found in the current
local variables.  Likewise, you can plot all numeric members contained
in a structure by selecting it, followed by `Plot'.

   If you want more control about what to include in a plot and what
not, you can use _display clusters_ (Note: Clustering).  A common
scenario is to plot a one-dimensional array together with the current
index position.  This is done in three steps:

  1. Display the array and the index, using `Display'.

  2. Cluster both displays: select them and choose `Undisp => Cluster
     ()'.

  3. Plot the cluster by pressing `Plot'.

   Scalars that are displayed together with arrays can be displayed
either as vertical lines or horizontal lines.  By default, scalars are
plotted as horizontal lines.  However, if a scalar is a valid index for
an array that was previously plotted, it is shown as a vertical line.
You can change this initial orientation by selecting the scalar
display, followed by `Rotate'.