Contour lines

### 17.5.1 Contour lines

The plotcontour or DrwCtour or contourplot command draws contour lines for functions of two variables.

- plotcontour takes two mandatory arguments and one optional argument:
  - expr, an expression involving two variables.
  - vars, a list of the two variables.
  - Optionally, values, a list of values of the contour lines to draw; expr=value, for value in values (by default, [−10,−8,…,8,10]).
- plotcontour(expr,vars ⟨,values ⟩) draws the contour lines expr=value for value in values.

#### Examples

plotcontour(x^2+y^2,[x=-3..3,y=-3..3],[1,2,3],display=[green,red,black]+[filled$3])

plotcontour(x^2-y^2,[x,y])

If you want to draw the surface in 3D representation, use plotfunc (see Section 17.2.2).

plotfunc(x^2-y^2,[x,y])