Easy Question, update scatter point in loop

Hi:

I just want to get the 4 vectors scatter update every time in my loop. Delete the last time points then plot then hold on to new loop.

How to do that??

Thank you.

x1{1} = [.2; .3]; x2{1} = [.3; .4]; x3{1} = [.5; .6]; x4{1} = [.6; .7]; k = 1;

for k = 1:1:50

    scatter(x1{k}(1,1), x1{k}(2,1));
    hold on
    scatter(x2{k}(1,1), x2{k}(2,1));
    hold on 
    scatter(x3{k}(1,1), x3{k}(2,1));
    hold on
    scatter(x4{k}(1,1), x4{k}(2,1));

    x1{k+1} = (x1{k} + x2{k} + x4{k})/3;
    x2{k+1} = (x1{k} + x2{k} + x3{k})/3;
    x3{k+1} = (x2{k} + x3{k} + x4{k})/3;
    x4{k+1} = (x1{k} + x3{k} + x4{k})/3;
end

Answer 1

[Ben11]

What if you try this:

x1{1} = [.2; .3]; x2{1} = [.3; .4]; x3{1} = [.5; .6]; x4{1} = [.6; .7]; k = 1;
figure
for k = 1:1:50

hold all
    scatter(x1{k}(1,1), x1{k}(2,1))

      scatter(x2{k}(1,1), x2{k}(2,1));

      scatter(x3{k}(1,1), x3{k}(2,1));

      scatter(x4{k}(1,1), x4{k}(2,1));
      x1{k+1} = (x1{k} + x2{k} + x4{k})/3;
      x2{k+1} = (x1{k} + x2{k} + x3{k})/3;
      x3{k+1} = (x2{k} + x3{k} + x4{k})/3;
      x4{k+1} = (x1{k} + x3{k} + x4{k})/3;
  hold off
  drawnow
  end

First you create a figure, then you force the plot to update with drawnow. You can keep the original "hold on" calls and see what it does as well.

[Yuang]

It can not delete the previous points. I want to delete the old points and plot new points.

[Ben11]

ok I'm not sure I understand then. What is the difference between old and previous points?

[Yuang]

Same. I mean I just want to plot x1(k), x2(k), x3(k), x4(k). And I update the data to x1(k+1), x2(k+1),x3(k+1),x4(k+1). To next loop, delete the last time x1,x2,x3,x4 points on graph, update plot the new 4 points.

I want to see the 4 points on one graph are moving. They should go to same place at last.

[Ben11]

ok. So is it something like this?:

x1{1} = [.2; .3]; x2{1} = [.3; .4]; x3{1} = [.5; .6]; x4{1} = [.6; .7]; k = 1;
figure
for k = 1:1:50

      scatter(x1{k}(1,1), x1{k}(2,1))
      hold on
      scatter(x2{k}(1,1), x2{k}(2,1));
      hold on
      scatter(x3{k}(1,1), x3{k}(2,1));
      hold on
      scatter(x4{k}(1,1), x4{k}(2,1));
      x1{k+1} = (x1{k} + x2{k} + x4{k})/3;
      x2{k+1} = (x1{k} + x2{k} + x3{k})/3;
      x3{k+1} = (x2{k} + x3{k} + x4{k})/3;
      x4{k+1} = (x1{k} + x3{k} + x4{k})/3;
  hold off
  drawnow
  end

[Yuang]

Yes. I think that's right. Can you slow down these points moving speed?

[Ben11]

You could add this line:

pause(n)

right after drawnow, where n is the time in seconds during which execution is paused.

[Yuang]

Thank you very much!!!! It help me a lot.

[Ben11]

Great! You're welcome.

[Yuang]

Sorry, one last question, do you know how to add a trial for points?

[Ben11]

Hum I'm don't know what a trial for points is sorry. Do you have an example?

[Yuang]

Sorry. I mean I want the figure shows the path x1,x2,x3 and x4 go.

[Ben11]

ok. Do you mean something like this:

for k = 1:50

      scatter(x1{k}(1,1), x1{k}(2,1))

      if k > 1    
          line([x1{k-1}(1,1) x1{k}(1,1)],[x1{k-1}(2,1) x1{k}(2,1)],'Color','r');
      end
      drawnow
      hold on

      scatter(x2{k}(1,1), x2{k}(2,1));
      if k > 1    
          line([x2{k-1}(1,1) x2{k}(1,1)],[x2{k-1}(2,1) x2{k}(2,1)],'Color','g');
      end
      drawnow
      hold on

      scatter(x3{k}(1,1), x3{k}(2,1));
      if k > 1    
          line([x3{k-1}(1,1) x3{k}(1,1)],[x3{k-1}(2,1) x3{k}(2,1)],'Color','b');
      end
      drawnow
      hold on

      scatter(x4{k}(1,1), x4{k}(2,1));
      if k > 1    
          line([x4{k-1}(1,1) x4{k}(1,1)],[x4{k-1}(2,1) x4{k}(2,1)],'Color','k');
      end
      drawnow
      hold on
      x1{k+1} = (x1{k} + x2{k} + x4{k})/3;
      x2{k+1} = (x1{k} + x2{k} + x3{k})/3;
      x3{k+1} = (x2{k} + x3{k} + x4{k})/3;
      x4{k+1} = (x1{k} + x3{k} + x4{k})/3;
  hold off
  pause(.1)
  end

I seems odd is it what you would expect?

Answer 2

[Geoff Hayes]

Try grabbing the handle returned from each scatter call and then deleting that on subsequent iterations. Outside the for loop declare an array to manage the scatter plot handles

 % declare an array for the handles to the scatter plots
 scatterHandles = [];

Now within the for loop, delete the handles if any exist

 for k = 1:1:50

     % delete scatter plot data from previous iteration if it exists
     if ~isempty(scatterHandles)
         for m=1:length(scatterHandles)
             delete(scatterHandles(m));
         end
     end

     % get the scatter plot handles for each call to scatter
      hold on
      scatterHandles (1) = scatter(x1{k}(1,1), x1{k}(2,1));
      scatterHandles (2) = scatter(x2{k}(1,1), x2{k}(2,1));
      scatterHandles (3) = scatter(x3{k}(1,1), x3{k}(2,1));
      scatterHandles (4) = scatter(x4{k}(1,1), x4{k}(2,1));

     % etc.
  end

Try the above and see what happens!