MATLAB Function Reference
ezcontour

Easy to use contour plotter

Syntax

• ```ezcontour(fun)
ezcontour(fun,domain)
ezcontour(...,n)
ezcontour(axes_handle,...)
h = ezcontour(...)
```

Description

`ezcontour(fun)` plots the contour lines of `fun(x,y)` using the `contour` function. `fun` is plotted over the default domain: -2 < x < 2, -2 < y < 2.

`fun` can be a function handle for an M-file function or an anonymous function (see Function Handles and Anonymous Functions) or a string (see the Remarks section).

```ezcontour(fun,domain) ``` plots `fun(x,y)` over the specified `domain`. `domain` can be either a 4-by-1 vector [`xmin`, `xmax`, `ymin`, `ymax`] or a 2-by-1 vector [`min`, `max`] (where `min` < x < `max`, `min` < y < `max`).

```ezcontour(...,n) ``` plots `fun` over the default domain using an `n`-by-`n` grid. The default value for `n` is 60.

```ezcontour(axes_handle,...) ``` plots into the axes with handle `axes_handle` instead of the current axes (`gca`).

```h = ezcontour(...) ``` returns the handles to contour objects in `h`.

`ezcontour` automatically adds a title and axis labels.

Remarks

Passing the Function as a String

Array multiplication, division, and exponentiation are always implied in the string expression you pass to `ezcontour`. For example, the MATLAB syntax for a contour plot of the expression

• ```sqrt(x.^2 + y.^2)
```

is written as

• ```ezcontour('sqrt(x^2 + y^2)')
```

That is, `x^2` is interpreted as `x.^2` in the string you pass to `ezcontour`.

If the function to be plotted is a function of the variables u and v (rather than x and y), then the domain endpoints `umin`, `umax`, `vmin`, and `vmax` are sorted alphabetically. Thus, `ezcontour('u^2 - v^3',[0,1],[3,6])` plots the contour lines for u2 - v3 over 0 < u < 1, 3 < v < 6.

Passing a Function Handle

Function handle arguments must point to functions that use MATLAB syntax. For example, the following statements define an anonymous function and pass the function handle `fh` to `ezcontour`.

• ```fh = @(x,y) sqrt(x.^2 + y.^2);
ezcontour(fh)
```

Note that when using function handles, you must use the array power, array multiplication, and array division operators (`.^, .*, ./`) since `ezcontour` does not alter the syntax, as in the case with string inputs.

If your function has additional parameters, for example `k` in `myfun`:

• ```function z = myfun(x,y,k)
z = x.^k - y.^k - 1;
```

then you can use an anonymous function to specify that parameter:

• ```ezcontour(@(x,y)myfun(x,y,2))
```

Examples

The following mathematical expression defines a function of two variables, x and y.

`ezcontour` requires a function handle argument that expresses this function using MATLAB syntax. This example uses an anonymous function, which you can define in the command window without creating an M-File.

• ```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);
```

For convenience, this function is written on three lines. See the peaks

Pass the function handle `f` to `ezcontour` along with a domain ranging from -3 to 3 in both `x` and `y` and specify a computational grid of 49-by-49:

• ```ezcontour(f,[-3,3],49)

```

In this particular case, the title is too long to fit at the top of the graph, so MATLAB abbreviates the string.

`contour`, `ezcontourf`, `ezmesh`, `ezmeshc`, `ezplot`, `ezplot3`, `ezpolar`, `ezsurf`, `ezsurfc`, `function_handle`