Creating a point moving along a graph in MATLAB

Question

I am looking to create a simple log(x) graph within MATLAB in which the model shows the point moving along the curve with time.

The overall aim is to have two of these graphs alongside one another and to apply an algorithm to them. I am really unsure where to start here.

I am relatively new at MATLAB coding so any help would be very useful!

Thanks Luke

Solution 1

Here is a variation on @Jacob's solution. Instead of redrawing everything at each frame (clf) we simply update the point's location:

%# control animation speed
DELAY = 0.01;
numPoints = 600;

%# create data
x = linspace(0,10,numPoints);
y = log(x);

%# plot graph
figure('DoubleBuffer','on')                  %# no flickering
plot(x,y, 'LineWidth',2), grid on
xlabel('x'), ylabel('y'), title('y = log(x)')

%# create moving point + coords text
hLine = line('XData',x(1), 'YData',y(1), 'Color','r', ...
    'Marker','o', 'MarkerSize',6, 'LineWidth',2);
hTxt = text(x(1), y(1), sprintf('(%.3f,%.3f)',x(1),y(1)), ...
    'Color',[0.2 0.2 0.2], 'FontSize',8, ...
    'HorizontalAlignment','left', 'VerticalAlignment','top');

%# infinite loop
i = 1;                                       %# index
while true      
    %# update point & text
    set(hLine, 'XData',x(i), 'YData',y(i))   
    set(hTxt, 'Position',[x(i) y(i)], ...
        'String',sprintf('(%.3f,%.3f)',[x(i) y(i)]))        
    drawnow                                  %# force refresh
    %#pause(DELAY)                           %# slow down animation

    i = rem(i+1,numPoints)+1;                %# circular increment
    if ~ishandle(hLine), break; end          %# in case you close the figure
end

Solution 2

A simple solution is:

x = 1:100;
y = log(x);
DELAY = 0.05;
for i = 1:numel(x)
    clf;
    plot(x,y);
    hold on;
    plot(x(i),y(i),'r*');
    pause(DELAY);
end

Solution 3

You may want to have a look at the COMET function, which will make an animation of the curve.

For example (using the same numbers as @Jacob)

x = 1:100;
y = log(x);
comet(x,y)

If you want to show the point moving on the line (not 'drawing' it), you simply plot the line before

x = 1:100;
y = log(x);
plot(x,y,'r')
hold on %# to keep the previous plot
comet(x,y,0) %# 0 hides the green tail

Comments

[knk]

+1 I didn't know about comet. BTW, if comet seems to do nothing try with more points (eg x=1:.01:100;)

[Christos]

Ben please be more descriptive.

[gnovice]

This adds nothing new that isn't already covered in Jonas' answer.

[mike]

Which is not a good solution, since you clear the whole figure each time an redraw literally everything. So speed, room for expansion etc. are not the best this way.