CODEWITHSUNDEEP
matlabmatlab-figure
Victor Pira
Victor Pira

Reputation: 1172

Plotting just the endpoint of quiver

I need to plot a block of points with small deviations from their equilibrium states. Using quiver it would look like this:

enter image description here

And now I want to plot just markers located on the arrow tips. How to do that?

Input data are U and V deviations (on cartesian axes), getting the X,Y coordinates of vector origins is not a problem.

Upvotes: 1

Views: 1135

Answers (1)

Luis Mendo
Luis Mendo

Reputation: 112679

You can't simply use something like plot(X+U, Y+V, 'o') because quiver applies an automatically computed scale to U and V so that all arrows fit nicely in the figure. You need to include that scale.

Looking into quiver's code and replicating the part that computes that scale, you can proceed as follows:

%// Example data
x = rand(1,20);
y = rand(1,20);
u = rand(1,20);
v = rand(1,20);

%// Taken from "quiver.m". Computes autoscale
if min(size(x))==1, n=sqrt(numel(x)); m=n; else [m,n]=size(x); end
delx = diff([min(x(:)) max(x(:))])/n;
dely = diff([min(y(:)) max(y(:))])/m;
del = delx.^2 + dely.^2;
if del>0
    len = sqrt((u.^2 + v.^2)/del);
    maxlen = max(len(:));
else
    maxlen = 0;
end
if maxlen>0
    autoscale = 0.9 / maxlen;
else
    autoscale = 0.9;
end

%// quiver plot
quiver(x, y, u, v)
hold on

%// plot marker at arrow tips, including computed autoscale
plot(x+autoscale*u, y+autoscale*v, 'o')

If you specify a scale argument to quiver, that argument is a factor that multiplies the internally computed scale. So you have to include that in plot as well:

%// quiver plot including manual scale factor
quiver(x, y, u, v, .5)
hold on

%// plot marker at arrow tips, including computed autoscale and manual scale
plot(x+.5*autoscale*u, y+.5*autoscale*v, 'o')

enter image description here

Upvotes: 3

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