MATLAB: HOw can I change the size of the arrows

fieldvector

I did this code to plot a vector field, and i was wondering how can i change the size of the arrows?

 t1 = linspace(-1,100,20);
y1 = linspace(-1,150,20);
[T,Y]=meshgrid(t1,y1);
DY=TribMod1(T,Y); DT=ones(size(DY));
scale =  1./sqrt(DT.^2+DY.^2);
quiver(T,Y, scale.*DT, scale.*DY);
axis([-1 100 -1 151])
ylabel('y')
xlabel('time (t)')
title('Direction field of function(1) with b=0.005')

Best Answer

Use the 'AutoScaleFactor' property:

% CREATE DATA: 
a = linspace(0,6*pi);
x = exp(-0.1*a) .* cos(a);
y = exp(-0.1*a) .* sin(a);
da = diff([0 a]);
dxda = diff([0 x]) ./ da;
dyda = diff([0 y]) ./ da;
% PLOT: 
figure(1)
subplot(2,1,1)
h1 = quiver(x, y, dxda, dyda)
set(h1,'AutoScale','on', 'AutoScaleFactor', 2)
axis equal square
title('Arrows 2')
subplot(2,1,2)
h2 = quiver(x, y, dxda, dyda)
set(h2,'AutoScale','on', 'AutoScaleFactor',0.5)
axis equal square
title('Arrows ½')

produces:

Related Solutions

MATLAB: How to indentify the variables when plotting after solving a coupled system of ODEs

The easiest way is to ask for a second output from your odeToVectorField call. It tells you the substitutions the function made to define each element in the returned column:

[yode,Sbs] = odeToVectorField(eqns);

here, the substitutions are:

Sbs =
  y
 Dy
  x
 Dx
  z
 Dz

The columns of ‘Yodefcn’ exactly reproduces those returned by odeToVectorField, and ode45 returns them in that order.

That can be used with some other assignments to automatically produce a legend that labels every line in the plot.

The Code —

syms x(t) y(t) z(t) p(t) Y
p=sin((0.5+3.5*t)*t);
D1y = diff(y,t);
D2y = diff(y,t,2);
D1x = diff(x,t);
D2x = diff(x,t,2);
D1z = diff(z,t);
D2z = diff(z,t,2);
eqns=[D2x+2*x-1*y==p,D2y+(0.5*10*exp(-10*t))*D1y-x+2*y-z==0,D2z-y+2*z==0];
[yode,Sbs] = odeToVectorField(eqns);
Yodefcn = matlabFunction(yode, 'Vars',[t Y]);
tspan = (0:0.001:10);
Y0 = [0 0,0 0,0 0];
[T,Y] = ode45(Yodefcn, tspan, Y0);
plot(T, Y)
Lgndc = sym2cell(Sbs);
Lgnds = regexp(sprintf('%s\n', Lgndc{:}), '\n', 'split');
legend(Lgnds(1:end-1), 'Location','N')

The Plot —

MATLAB: How does QUIVER scale the vectors it plots

There are two independent scaling operations that occur when making a Quiver plot. First, the lengths of the arrows are scaled to fit within the plot area without overlapping. Next, scaling is performed as determined by the 'AutoScale' and 'AutoScaleFactor' properties.

Unfortunately, there is no way to retrieve the scale factor that is applied internally in the first scaling operation of the QUIVER command.

As a workaround, it is possible to create a Quiver plot with arrows scaled by a known amount by turning off the 'AutoScale' option. The U- and V- data can be scaled manually as necessary to improve the aesthetics of the plot. By performing this scaling manually, a known scale factor can be used. For example,

x = [0 0]
y = [0 10]
u = [10 0]
v = [0 10]
quiver(x,y,u,v)

produces arrows with lengths of about 6.364. To get better control over these lengths, manually scale the vectors:

scale_factor = 0.5;
quiver(x,y,u*scale_factor,v*scale_factor,'AutoScale','off')

The commands produce arrows of length 5.

Best Answer

Related Solutions

MATLAB: How to indentify the variables when plotting after solving a coupled system of ODEs

MATLAB: How does QUIVER scale the vectors it plots

Related Question