contour2d - level curves of a surface on a 2D plot
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")
contour2d draws level curves of a surface z=f(x,y) on a 2D plot. The values of f(x,y) are given by the matrix z at the grid points defined by x and y .
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. This last feature is useful in conjunction with legends to display the level numbers in a legend and not directly onto the level curves as usual (see Examples).
The optional arguments style,strf,leg,rect,nax , can be passed by a sequence of statements key1=value1, key2=value2 , ... where keys may be style , strf , leg , rect , nax . In this case, the order has no special meaning.
Use contour to draw levels curves on a 3D surface.
contour2d(1:10,1:10,rand(10,10),5,rect=[0,0,11,11])
// changing the format of the printing of the levels
xset("fpf","%.2f")
clf()
contour2d(1:10,1:10,rand(10,10),5,rect=[0,0,11,11])
// now an example with level numbers drawn in a legend
// Caution there are a number of tricks...
x = linspace(0,4*%pi,80);
z = cos(x')*cos(x);
clf(); f=gcf();
xset("fpf"," ") // trick 1: this implies that the level numbers are not
// drawn on the level curves
f.color_map=jetcolormap(7);
// trick 2: to be able to put the legend on the right without
// interfering with the level curves use rect with a xmax
// value large enough
contour2d(x,x,z,-0.75:0.25:0.75,frameflag=3,rect=[0,0,5*%pi,4*%pi])
// trick 3: use legends (note that the more practical legend function
// will not work as soon as one of the level is formed by 2 curves)
legends(string(-0.75:0.25:0.75),1:7,"lr");
xtitle("Some level curves of the function cos(x)cos(y)")
contour , fcontour , fcontour2d , contour2di , plot2d , xset ,
J.Ph.C.