getvariables returns the internal index associated with an sdpvar variable

```
k = getvariables(x)
```

sdpvar variables are built-up from internal variable indicies (i.e., the only internal name and reference is an integer).

```
yalmip('clear')
x = sdpvar(1);
getvariables(x)
ans =
1
y = sdpvar(2,3);
getvariables(y)
ans =
2 3 4 5 6 7
```

Also nonlinear terms have internal indicies (and assosciated structures to explain how the term relates to other linear variables)

```
z = x^2;
getvariables(z)
ans =
8
```

Expressions are built up from variables

```
z = x + 3*x^2;
getvariables(z)
ans =
1 8
```

In most situations you typically use depends which returns the index to the involved linear variables.