### 3.2.2  3-d graph

plotfunc takes two main arguments : an expression of two variables or a list of several expressions of two variables and the list of these two variables, where each variable may be replaced by an equality variable=interval to specify the range for this variable (if not specified, default values are taken from the graph configuration). plotfunc accepts two optional arguments to specify the discretisation step in x and in y by xstep=... and ystep=.... Alternatively one can specify the number of points used for the representation of the function with `nstep=` (instead of `xstep` and ystep).
plotfunc draws the surface(s) defined by z= the first argument.
Input :

plotfunc( x`^`2+y`^`2,[x,y])

Output :

A 3D graph of z=x`^`2+y`^`2

Input :

plotfunc(x*y,[x,y])

Output :

The surface z=x*y, default ranges

Input :

plotfunc([x*y-10,x*y,x*y+10],[x,y])

Output :

The surfaces z=x*y-10, z=x*y and z=x*y+10

Input :

plotfunc(x*sin(y),[x=0..2,y=-pi..pi])

Output :

The surface z=x*y for the specified ranges

Now an example where we specify the x and y discretisation step with `xstep` and `ystep`. Input :

plotfunc(x*sin(y),[x=0..2,y=-pi..pi],xstep=1,ystep=0.5)

Output :

A portion of surface z=x*y

Alternatively we may specify the number of points used for the representation of the function with `nstep` instead of `xstep` and `ystep`, input :

plotfunc(x*sin(y),[x=0..2,y=-pi..pi],nstep=300)

Output :

A portion of surface z=x*y

Remarks

• Like any 3-d scene, the viewpoint may be modified by rotation around the x axis, the y axis or the z axis, either by dragging the mouse inside the graphic window (push the mouse outside the parallelepiped used for the representation), or with the shortcuts x, X, y, Y, z and Z.
• If you want to print a graph or get a LATEX translation, use the graph menu