Set hold on for some parts of a figure, not others

Question

Below is my matlab code that plots a black line as it rotates around the origin. For the most part the code works, but because I use 'hold on', once I plot a line, it stays there for the entirety of the program.

What I'd like is something more like a second hand on a clock (only moving counter clockwise). For a particular value of i, the black line prints, and after i increments, that previous line is gone. However, I would like the red and blue lines and the plotted text to stay on the plot from iteration to iteration. I tried using the set() command and couldn't get it working, any ideas?

scalar = 3;

a = [3/scalar 2/scalar];
b = [-4/scalar .5/scalar];

starts = zeros(2,2);
ends = [a;b];

hold on
quiver(0,0,a(1),a(2),'color',[0 0 1],'linewidth',3);
quiver(0,0,b(1),b(2),'color',[1 0 0],'linewidth',3);
axisSize = 15/scalar;
axis([-axisSize axisSize -axisSize axisSize])

mintheta = [500, 500];
%waitforbuttonpress
for i=1:360
    theta = [cos(2*pi()*i/360) sin(2*pi()*i/360)];
    minDot = min(a*theta',-1*(b*theta'));
    theta = theta/minDot;

    hold on
    if (minDot > 0)
        if (norm(theta) < norm(mintheta))
            mintheta = theta;
        end

        text(-4.5, 4, 'Drawing all Theta vectors,');
        text(-4.5, 3.7, 'according to constraint that');
        text(-4.5, 3.4, 'all dotProducts >= 1');
        text(-4.5, 2.5, 'Yellow indicates a non-separating plane,');
        text(-4.5, 2.2, 'SVM looks for shortest possible');
        text(-4.5, 1.9, 'Theta (will be shown in green).');
        quiver(0,0,theta(1),theta(2),'color',[0 0 0],'linewidth',5);
        quiver(0,0,3/scalar,2/scalar,'color',[0 0 1],'linewidth',3);
        quiver(0,0,-4/scalar,.5/scalar,'color',[1 0 0],'linewidth',3);
        axis([-axisSize axisSize -axisSize axisSize])
    else
        quiver(0,0,cos(2*pi()*i/360),sin(2*pi()*i/360),'color',[1 1 0],'linewidth',5);
    end

    pause(.05);
end
quiver(0,0,mintheta(1),mintheta(2),'color',[0 1 0],'linewidth',3);

onewhaleid onewhaleid · Accepted Answer · 2014-02-24T21:45:18

This should get you started:

% set up axis
axisSize = 5;
axis([-axisSize axisSize -axisSize axisSize])
cla

hold on

% draw quiver at initial position
q = quiver(0,0,cos(2*pi()*0/360),sin(2*pi()*0/360),'color',[0 0 0],'linewidth',5);

for i = 1:360

   % modify data inside quiver plot
   set(q,...
       'xdata',0,...
       'ydata',0,...
       'udata',cos(2*pi()*i/360),...
       'vdata',sin(2*pi()*i/360)) 

   pause(.05);
end

Also, I would put the text outside the loop. It only needs to be created once, and MATLAB doesn't render stacks of identical text very nicely for some reason.

Set hold on for some parts of a figure, not others

1 Answers