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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.