contour

Arguments

x,y

two real row vectors of size n1 and n2.

z

real matrix of size (n1,n2), the values of the function or a Scilab function which defines the surface z=f(x,y).

nz

the level values or the number of levels.

-

If nz is an integer, its value gives the number of level curves equally spaced from zmin to zmax as follows:

z= zmin + (1:nz)*(zmax-zmin)/(nz+1)

Note that the zmin and zmax levels are not drawn (generically they are reduced to points) but they can be added with

[im,jm] = find(z == zmin);     // or zmax 
plot2d(x(im)',y(jm)',-9,"000")

-

If nz is a vector, nz(i) gives the value of the ith level curve. Note that it can be useful in order to see zmin and zmax level curves to add an epsilon tolerance: nz=[zmin+%eps,..,zmax-%eps].

<opt_args>

a sequence of statements key1=value1, key2=value2, ... where keys may be theta,alpha,leg,flag, ebox,zlev (see below). In this case, the order has no special meaning.

theta, alpha

real values giving in degree the spherical coordinates of the observation point.

leg

string defining the captions for each axis with @ as a field separator, for example "X@Y@Z".

flag

a real vector of size three flag=[mode,type,box].

mode

string representation mode.

mode=0:

the level curves are drawn on the surface defined by (x,y,z).

mode=1:

the level curves are drawn on a 3D plot and on the plan defined by the equation z=zlev.

mode=2:

the level curves are drawn on a 2D plot.

type

an integer (scaling).

type=0

the plot is made using the current 3D scaling (set by a previous call to param3d, plot3d, contour or plot3d1).

type=1

rescales automatically 3d boxes with extreme aspect ratios, the boundaries are specified by the value of the optional argument ebox.

type=2

rescales automatically 3d boxes with extreme aspect ratios, the boundaries are computed using the given data.

type=3

3d isometric with box bounds given by optional ebox, similarily to type=1

type=4

3d isometric bounds derived from the data, to similarilytype=2

type=5

3d expanded isometric bounds with box bounds given by optional ebox, similarily to type=1

type=6

3d expanded isometric bounds derived from the data, similarily to type=2

box

an integer (frame around the plot).

box=0

nothing is drawn around the plot.

box=1

unimplemented (like box=0).

box=2

only the axes behind the surface are drawn.

box=3

a box surrounding the surface is drawn and captions are added.

box=4

a box surrounding the surface is drawn, captions and axes are added.

ebox

used when type in flag is 1. It specifies the boundaries of the plot as the vector [xmin,xmax,ymin,ymax,zmin,zmax].

zlev

real number.

Description

contour draws level curves of a surface z=f(x,y). The level curves are drawn on a 3D surface. The optional arguments are the same as for the function plot3d (except zlev) and their meanings are the same. They control the drawing of level curves on a 3D plot. Only flag(1)=mode has a special meaning.

mode=0

the level curves are drawn on the surface defined by (x,y,z).

mode=1

the level curves are drawn on a 3D plot and on the plan defined by the equation z=zlev.

mode=2

the level curves are drawn on a 2D plot.

You can change the format of the floating point number printed on the levels by using xset("fpf",string) where string gives the format in C format syntax (for example string="%.3f"). Use string="" to switch back to default format and Use string=" " to suppress printing.

Usually we use contour2d to draw levels curves on a 2D plot.

Enter the command contour() to see a demo.

Examples

t=linspace(-%pi,%pi,30);
function z=my_surface(x, y),z=x*sin(x)^2*cos(y),endfunction

contour(t,t,my_surface,10)
// changing the format of the printing of the levels
xset("fpf","%.1f")
clf()
contour(t,t,my_surface,10)
// 3D
clf()
z=feval(t,t,my_surface);
plot3d(t,t,z);contour(t,t,z+0.2*abs(z),20,flag=[0 2 4]);

See Also

• contour2d
• plot3d

Authors

J.Ph.C.