1.9.2 Options

When Mathematica plots a graph for you, it has to make many choices. It has to work out what the scales should be, where the function should be sampled, how the axes should be drawn, and so on. Most of the time, Mathematica will probably make pretty good choices. However, if you want to get the very best possible pictures for your particular purposes, you may have to help Mathematica in making some of its choices.

There is a general mechanism for specifying "options" in Mathematica functions. Each option has a definite name. As the last arguments to a function like Plot, you can include a sequence of rules of the form name->value, to specify the values for various options. Any option for which you do not give an explicit rule is taken to have its "default" value.

Plot[f, {x, , }, option->value]
	make a plot, specifying a particular value for an option

A function like Plot has many options that you can set. Usually you will need to use at most a few of them at a time. If you want to optimize a particular plot, you will probably do best to experiment, trying a sequence of different settings for various options.

Each time you produce a plot, you can specify options for it. Section 1.9.3 will also discuss how you can change some of the options, even after you have produced the plot.

option name	default value
AspectRatio	1/GoldenRatio	the height-to-width ratio for the plot; Automatic sets it from the absolute and coordinates
Axes	Automatic	whether to include axes
AxesLabel	None	labels to be put on the axes; ylabel specifies a label for the axis, {xlabel, ylabel} for both axes
AxesOrigin	Automatic	the point at which axes cross
TextStyle	$TextStyle	the default style to use for text in the plot
FormatType	StandardForm	the default format type to use for text in the plot
DisplayFunction	$DisplayFunction	how to display graphics; Identity causes no display
Frame	False	whether to draw a frame around the plot
FrameLabel	None	labels to be put around the frame; give a list in clockwise order starting with the lower axis
FrameTicks	Automatic	what tick marks to draw if there is a frame; None gives no tick marks
GridLines	None	what grid lines to include; Automatic includes a grid line for every major tick mark
PlotLabel	None	an expression to be printed as a label for the plot
PlotRange	Automatic	the range of coordinates to include in the plot; All includes all points
Ticks	Automatic	what tick marks to draw if there are axes; None gives no tick marks

This specifies labels for the and axes. The expressions you give as labels are printed just as they would be if they appeared as Mathematica output. You can give any piece of text by putting it inside a pair of double quotes.

In[9]:=  Plot[Sin[x^2], {x, 0, 3}, AxesLabel -> {"x value", "Sin[x^2]"} ] Out[9]=

Automatic	use internal algorithms
None	do not include this
All	include everything
True	do this
False	do not do this

When Mathematica makes a plot, it tries to set the and scales to include only the "interesting" parts of the plot. If your function increases very rapidly, or has singularities, the parts where it gets too large will be cut off. By specifying the option PlotRange, you can control exactly what ranges of and coordinates are included in your plot.

Automatic	show at least a large fraction of the points, including the "interesting" region (the default setting)
All	show all points
{, }	show a specific range of values
{xrange, yrange}	show the specified ranges of and values

The setting for the option PlotRange gives explicit limits for the graph. With the limits specified here, the bottom of the curve is cut off.

In[12]:=  Plot[Sin[x^2], {x, 0, 3}, PlotRange -> {0, 1.2}] Out[12]=

Mathematica always tries to plot functions as smooth curves. As a result, in places where your function wiggles a lot, Mathematica will use more points. In general, Mathematica tries to adapt its sampling of your function to the form of the function. There is, however, a limit, which you can set, to how finely Mathematica will ever sample a function.

The function wiggles infinitely often when . Mathematica tries to sample more points in the region where the function wiggles a lot, but it can never sample the infinite number that you would need to reproduce the function exactly. As a result, there are slight glitches in the plot.

In[13]:=  Plot[Sin[1/x], {x, -1, 1}] Out[13]=

option name	default value
PlotStyle	Automatic	a list of lists of graphics primitives to use for each curve (see Section 2.10.3)
PlotPoints	25	the minimum number of points at which to sample the function
MaxBend	10.	the maximum kink angle between successive segments of a curve
PlotDivision	30.	the maximum factor by which to subdivide in sampling the function
Compiled	True	whether to compile the function being plotted

It is important to realize that since Mathematica can only sample your function at a limited number of points, it can always miss features of the function. By increasing PlotPoints, you can make Mathematica sample your function at a larger number of points. Of course, the larger you set PlotPoints to be, the longer it will take Mathematica to plot any function, even a smooth one.

Since Plot needs to evaluate your function many times, it is important to make each evaluation as quick as possible. As a result, Mathematica usually compiles your function into a low-level pseudocode that can be executed very efficiently. One potential problem with this, however, is that the pseudocode allows only machine-precision numerical operations. If the function you are plotting requires higher-precision operations, you may have to switch off compilation in Plot. You can do this by setting the option Compiled -> False. Note that Mathematica can only compile "inline code"; it cannot for example compile functions that you have defined. As a result, you should, when possible, use Evaluate as described in Section 1.9.1 to evaluate any such definitions and get a form that the Mathematica compiler can handle.