Linked plots are graphs in figure windows
that visibly respond to changes in the current workspace variables
they display and vice versa. This differs from the default behavior
of graphs, which contain copies of variables they represent (their
and must be explicitly replotted in order to update them when a displayed
variable changes. For example, if variable y in
the workspace appears in a linked plot and y is
modified in the Command Window, the graphic representation of y in
the linked plot updates within half a second to reflect the change.
If you use the Variables editor, you might be familiar with data linking. When variables change or go out of scope, the Variables editor updates itself. It continuously updates variables in the workspace when you add, change, or delete values. The Variables editor works the same way with linked plots.
You can programmatically update a plot after the elements in
one variable change. For example, the following code calls
update the plot after
x = 0:.1:8*pi; y = sin(x); h = plot(x,y) set(h,'XDataSource','x'); set(h,'YDataSource','y'); y = sin(x.^3); refreshdata
refreshdatareference page. Prior to data linking, you need to explicitly update your plots to reflect changes in your workspace variables, as illustrated in Linking vs. Refreshing Plots.
If the same variable appears in plots in multiple figures, you can link any of the plots to the variable. You can use linked plots in concert with Marking Up Graphs with Data Brushing, but also on their own. Linking plots lets you
Make graphs respond to changes in variables in the base workspace or within a function
Make graphs respond when you change variables in the Variables editor and Command Line
Modify variables through data brushing that affect different graphical representations of them at once
Create graphical "watch windows" for debugging purposes
Watch windows are useful if you program in the MATLAB® language. For example, when refining a data processing algorithm to step through your code, you can see graphs respond to changes in variables as a function executes statements.
When you create a figure, by default, data linking is off. You can put a figure into a linked state in any of three ways:
Click the Data Linking tool button on the figure toolbar.
Select Link from the figure Tools menu.
linkdata MATLAB function,
To disable data linking, click the Data Linking tool
button, deselect Tools > Link, or type
Once a figure is linked, its appearance changes; an information bar, called the linked plot information bar, appears beneath the figure toolbar to reflect its new linked state. It identifies all linked variables and gives you an opportunity to unlink or relink any of them. The linked plot information bar identifies a figure as being linked and displays relationships between graphic objects and the workspace variables they represent. Click the circular down arrow icon on its left side to display a legend that identifies the data source for each graphic object in a graph.
For example, execute this code at the command line:
y = randn(10,3); plot(y)
Dropping down the linked plot legend is useful when many data
sources are linked to a graph at once. Like legends created with the
it identifies graph components with variable expressions.
Once linked to its data source(s), a figure acts as if you called
the MATLAB function
refreshdata every time
a workspace variable it displays changes. That is, any series or group
graphic objects contained in the figure can update its own
ZData properties and redraw itself when one
of its data sources is modified. If the linked state is set to
linkdata function, by deselecting the Data
Linking toolbar button, or by deselecting Link on
the figure's Tools menu, automatic refreshing
When you turn linking on for a figure, the linking mechanism can usually identify the data sources for displayed graphs, but sometimes ambiguity exists about what variable or range of a variable has been plotted. At such times, the Linked Plot information bar informs you that graphics have no data sources and gives you a chance to identify them. Click fix it to open a dialog box where you can specify the variables and ranges of any or all plotted variables.
For example, create a matrix of random data and plot a histogram of the fourth column.
x = rand(10); hist(x(:,4))
YDataSourceto choose the source of the data,
You can create graphs that have no data sources. For example,
When you brush a graph that is not linked to data sources, you brush the graphics only. The brushing affects only the figure you interact with. However, when you brush a linked plot, you are brushing the underlying variables. In this case, your brush marks also display on all linked plots that have the same data sources you brushed, as well as any display of that data which you have opened in the Variables editor. The color of the brush marks in all displays is the brush color you have selected for the figure in which you are brushing. This color can differ from the brush colors you have chosen to use in others display, and overrides those colors.
Besides the linked plots feature, other MATLAB mechanisms connect graphic objects to data sources (workspace variables). The main techniques are:
Directly update the
of a graph.
Set a graph's
For an example of updating object properties to animate graphics, see Trace Marker Along Line in the MATLAB Graphics documentation. Data linking is not a method intended for animating data graphs.
Linking plots automates these tasks and keeps graphs continuously
in sync with the variables they depict, making it the easiest technique
to use. Data sources must still exist in the workspace, but you do
not need to explicitly declare them for linked plots unless some ambiguity
exists. The following code examples iteratively approximate pi, and illustrate the difference between declaring
and refreshing data sources yourself and letting the
handle it for you.
|Updating a Graph with refreshdata||Updating a Graph with linkdata|
x1= [1 2]; y1 = [4 4]; ntimes = 100; denom = 1; k = -1; subplot(1,2,1) hp1 = plot(x1,y1); xlabel('Updated with REFRESHDATA') ylabel('\pi') set(gca,'Xlim',[0 ntimes],... 'Ylim',[2.5 4]) set(hp1,'XDataSource', 'x1') set(hp1,'YDataSource', 'y1') for t = 3:ntimes denom = denom + 2; x1(t) = t; y1(t) = 4*(y1(t-1)/4 + k/denom); refreshdata drawnow k = -k; end line([0 ntimes], [pi pi],'color','c')
x2= [1 2]; y2 = [4 4]; ntimes = 100; denom = 1; k = -1; subplot(1,2,2) plot(x2,y2); xlabel('Updated with LINKDATA') ylabel('\pi') set(gca,'Xlim',[0 ntimes],... 'Ylim',[2.5 4]) linkdata on for t = 3:ntimes denom = denom + 2; x2(t) = t; y2(t) = 4*(y2(t-1)/4 + k/denom); k = -k; end line([0 ntimes], [pi pi],'color','c')
Differences are shown in italics.
When you execute the code on the left, which uses
it animates the approximation process. The code on the right uses
does not animate; it runs much faster. (A
is not needed, because data linking buffers update and refresh the
graph at half-second intervals.) The graphic results, shown in the
next image, are identical. Because both plots are in axes in the same
figure, linking the second graph also links the first graph to its
To minimize the Linked Plot information bar while remaining
in linked mode, click the hide/show button
on its right side; the button flips
direction and the bar is hidden. Clicking the button again flips the
arrow back and restores the Linked Plot information bar. Turning off
linking cuts all data source connections and removes the Linked Plot
information bar from the figure. However, the data source properties
remain set, and the bar reappears whenever a linked state is restored
by selecting Tools > Link, depressing the Linked Plot button,
or calling the
linkdata function. Whatever data
sources were established previously will then reconnect (assuming
those variables still exist in the same form).
down arrow button on the left side
of the Linked Plot information bar drops down a legend (similar to
legend function produces but without
Display Names). The legend identifies workspace variables associated
with plot objects for the entire figure (
on a per-axes basis), such as these linked lineseries from the previous
example, shown in the next image.
The drop-down legend names variable linked to the graphic objects
in the figure. For items to appear there, a graph must have an
ZDataSource property that MATLAB can
evaluate without error. The icon for each list entry reflects the
the corresponding graphic object, making clear which graphic objects
link to which variables. The drop-down legend is informational only;
you can only dismiss it after reading it by clicking anywhere else
on the figure.
Clicking the Edit link on the information
bar opens the Specify Data Source Properties modal dialog box for
you to set the
ZDataSource properties of plot objects in
the figure to columns or vectors of workspace variables. Changing
DisplayName updates text on a legend, if present
for the variable, and has no other effects. The three columns on the
right contain drop-down lists of workspace variables. You can also
type variable names and ranges, or a MATLAB expression. When
you change variables or their ranges on the fly with this dialog box,
variables plotted against one another must be compatible types and
have the same number of observations (as in any bivariate graph).
If you attempt to link a plot and
identify more than one possible workspace variable for one or more
plot objects, the Specify Data Source Properties dialog box appears
for you to resolve the ambiguity. If you choose not to or are unable
to do so and cancel the dialog box, data linking is not established
for those graphic objects.
Updating a linked plot can fail if the strings in the
ZDataSource properties are incompatible with
what is in the current workspace. Consequently, the corresponding
ZData cannot be updated. This happens most
often because variables are cleared or no longer exist when the workspace
changes (e.g., when you are debugging).
However, failing links do not affect the visual appearance of the object in the graph. Instead, a warning icon and message appears on the Linked Plot information bar when this occurs for any plotted data in the figure. The failing link warning is general, but you can identify which variables are affected by clicking the Data Source button. If you hide the Linked Plot information bar (by clicking its Hide button), the bar reappears when a data links fails, alerting you to the issue.