champ

Arguments

x, y

vectors of decimal numbers, which define the grid of nodes = coordinates of arrows starting points.

fx

a matrix which describes the x component of the vector field. fx(i,j) is the x component of the vector field at point (x(i),y(j)).

fy

a matrix which describes the y component of the vector field. fy(i,j) is the y component of the vector field at point (x(i),y(j)).

<opt_args>

This represents a sequence of statements key1=value1, key2=value2,... where key1, key2,... can be one of the following: arfact, rect, strf (see below).

arfact

an optional argument of type real which gives a scale factor for the display of the arrow heads on the plot (default value is 1.0).

rect

a vector rect=[xmin, ymin, xmax, ymax] which gives the boundaries of the graphics frame to use.

strf

a string of length 3 "xyz" which has the same meaning as the strf parameter of plot2d. The first character x has no effect with champ.

Description

champ(…) plots a field of 2D vectors with arrows.

By default, all arrows have the same color, and their length is proportional to the local intensity of the field (norm of vectors). In addition, all lengths are normalized according to the longest arrow.

When setting gce().colored = "on", each arrow becomes as long as possible in its cell, and is colored according to the local intensity of the field.

After calling champ(…), gce() returns the handle of the field of arrows, of type Champ, whose properties can be post-processed.

Enter the command champ() to see an example.

Examples

x = -4:6;
X = ndgrid(x);
[fx, fy] =  (rand(X)-0.5, rand(X)-0.5);

clf
gcf().color_map = jetcolormap(50);

// Field's intensity = arrows length
subplot(2,2,1)
champ(x, x, fx, fy)

// With bigger arrow heads
subplot(2,2,2)
champ(x, x, fx, fy, arfact=1.7)
title("arfact=1.7", "fontsize",3)

// Field's intensity = arrows color
xsetech([0 0.5 0.55 0.5])
champ(x, x, fx, fy, arfact=1.7)
gce().colored = "on";
title("arfact=1.7, .colored=""on""", "fontsize",3)
colorbar

// Field's intensity = color, + imposed boundaries
subplot(2,2,4)
champ(x, x, fx, fy, rect=[-5,-6,9,7],strf="011")
gce().colored = "on";
title("rect=[-5,-6,9,6], strf=""011"", .colored=""on""", "fontsize",3)

gcf().axes_size = [740 680];

x = -1.2:0.11:0.7;
y = -1:0.11:0.5;
[X, Y] = ndgrid(x, y);
[fx, fy] = (2*X, 2*Y);

clf
xsetech([0 0 0.45 1])
champ(x, y, fx, fy)
title(".colored = ""off"" (default)", "fontsize",3)
xsetech([0.45 0 0.55 1])
champ(x, y, fx, fy)
title(".colored = ""on""", "fontsize",3)
gce().colored = "on";

gcf().color_map = jetcolormap(100);
colorbar

See also

• champ_properties — description of the 2D vector field entity properties
• fchamp — direction field of a 2D first order ODE
• xarrows — dessine un ensemble de flèches en 2D ou 3D.
• Arrowed polyline — description of the Polyline entity properties