fgrayplot 2D plot of a surface defined by a function using colors

## Syntax

    fgrayplot(x,y,f,[strf,rect,nax])
                fgrayplot(x,y,f,<opt_args>)

## Arguments

x,y

  real row vectors.

f

  external of type `y=f(x,y)`.

<opt_args>

  This represents a sequence of statements `key1=value1, key2=value2`,... where `key1`, `key2,...` can be one of the following: rect, nax, strf or axesflag and frameflag (see `plot2d`).

strf,rect,nax

  see `plot2d`.

## Description

`fgrayplot` makes a 2D plot of the surface given by `z=f(x,y)` on a grid defined by `x` and `y`. Each rectangle on the grid is filled with a gray or color level depending on the average value of `z` on the corners of the rectangle.

Enter the command `fgrayplot()` to see a demo.

## Examples

    t=-1:0.1:1;
    deff("[z]=my_surface(x,y)","z=x**2+y**2")
    fgrayplot(t,t,my_surface,rect=[-2,-2,2,2])

t=-1:0.1:1; deff("[z]=my_surface(x,y)","z=x**2+y**2") fgrayplot(t,t,my_surface,rect=[-2,-2,2,2])

## See also

- grayplot
- plot2d
- Sgrayplot
- Sfgrayplot