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### 15.1.8 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.

Function File: sombrero (n)

Produce the familiar three-dimensional sombrero plot using n grid lines. If n is omitted, a value of 41 is assumed.

The function plotted is

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

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

Generate 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 `mesh`. If n is a scalar, the `peaks` returns the values of the above function on a 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 x and y values of the grid on which to calculate the above function. The x and y values can be specified separately.

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