### `plot3d`: Plot 3-d surface plot

 ``` plot3d ```(x, y, z, nx, ny, opt, side);

Plots a three dimensional surface plot within the environment set up by `plw3d`. The surface is defined by the two-dimensional array `z`[`nx`][`ny`], the point `z`[i][j] being the value of the function at (`x`[i], `y`[j]). Note that the points in arrays `x` and `y` do not need to be equally spaced, but must be stored in ascending order. The parameter `opt` controls the way in which the surface is displayed. For further details see the Section called Three Dimensional Surface Plots in Chapter 3. The only difference between `plmesh` and `plot3d` is that `plmesh` draws the bottom side of the surface, while `plot3d` only draws the surface as viewed from the top.

 `x` (PLFLT *, input) Pointer to set of x coordinate values at which the function is evaluated. `y` (PLFLT *, input) Pointer to set of y coordinate values at which the function is evaluated. `z` (PLFLT **, input) Pointer to a vectored two-dimensional array with set of function values. `nx` (PLINT, input) Number of `x` values at which function is evaluated. `ny` (PLINT, input) Number of `y` values at which function is evaluated. `opt` (PLINT, input) Determines the way in which the surface is represented: `opt`=DRAW_LINEX: Lines are drawn showing `z` as a function of `x` for each value of `y`[j]. `opt`=DRAW_LINEY: Lines are drawn showing `z` as a function of `y` for each value of `x`[i]. `opt`=DRAW_LINEXY: Network of lines is drawn connecting points at which function is defined. `side` (PLBOOL, input) Flag to indicate whether or not ``sides'' should be draw on the figure. If `side` is true sides are drawn, otherwise no sides are drawn.

Redacted form: `plot3d(x, y, z, opt, side)`

This function is used in examples 11,21.