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# Time for action – making a surface plot

1. First we define the domain:
```octave:102> x = [-2:0.1:2]; y = x;
```
2. Then we generate the mesh grids:
```octave:103> [X Y] = meshgrid(x,y);
```
3. We can now calculate the range of f for all combinations of x and y values in accordance with Equation (3.4):
```octave:104> Z = X.^2 – Y.^2;
```
4. To make a surface plot of the graph we use:
```octave:105> surface(X,Y, Z)
```

The result is shown below:

## What just happened?

In Command 103, `X` is simply a matrix, where the rows are copies of `x`, and `Y` is a matrix where the columns are copies of the elements in `y`. From `X` and `Y`, we can then calculate the range as done in Command 104. We see that `Z`

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