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# champ

plots as arrows a field of 2D vectors

### Syntax

champ() // example champ(x, y, fx, fy) champ(x, y, fx, fy, arfact) champ(x, y, fx, fy, arfact, rect) champ(x, y, fx, fy, arfact, rect, strf) champ(x, y, fx, fy, <opt_args>)

### 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

## Comments

Author :Hervé Rabs posted the 31/05/2014 00:04where are the first component and the second component from champ(x,x,Fx,Fy) when

we draw different arrows in the graph ?( How to create arrows in the graph ?)

I have already looked for a forum in this site but I can't and I am sorry to write my question here.

Yours faithfully,

Hervé Rabs

e-mail: quarantebond@yahoo.fr

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