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#### 15.2.11 Test Plotting Functions

The functions `sombrero` and `peaks` provide a way to check that plotting is working. Typing either `sombrero` or `peaks` at the Octave prompt should display a three-dimensional plot.

: sombrero ()
: sombrero (n)
: z = sombrero (…)
: [x, y, z] = sombrero (…)

Plot the familiar 3-D sombrero function.

The function plotted is

```z = sin (sqrt (x^2 + y^2)) / (sqrt (x^2 + y^2))
```

Called without a return argument, `sombrero` plots the surface of the above function over the meshgrid [-8,8] using `surf`.

If n is a scalar the plot is made with n grid lines. The default value for n is 41.

When called with output arguments, return the data for the function evaluated over the meshgrid. This can subsequently be plotted with `surf (x, y, z)`.

: peaks ()
: peaks (n)
: peaks (x, y)
: z = peaks (…)
: [x, y, z] = peaks (…)

Plot a function with lots of local maxima and minima.

The function has the form

```f(x,y) = 3*(1-x)^2*exp(-x^2 - (y+1)^2) ...
- 10*(x/5 - x^3 - y^5)*exp(-x^2-y^2) ...
- 1/3*exp(-(x+1)^2 - y^2)
```

Called without a return argument, `peaks` plots the surface of the above function using `surf`.

If n is a scalar, `peaks` plots the value of the above function on an n-by-n mesh over the range [-3,3]. The default value for n is 49.

If n is a vector, then it represents the grid values over which to calculate the function. If x and y are specified then the function value is calculated over the specified grid of vertices.

When called with output arguments, return the data for the function evaluated over the meshgrid. This can subsequently be plotted with `surf (x, y, z)`.