Giving a moving point a chance to change path every step?

Here is the current code I have working, but simply put it will randomise 4 coordinates, b, c, d and e, and then animate drawing a line connecting each of them in a given number of steps.

b1 = randi([0 7e5])
b2 = randi([0 7e5])
c1 = randi([0 7e5])
c2 = randi([0 7e5])
d1 = randi([0 7e5])
d2 = randi([0 7e5])
e1 = randi([0 7e5])
e2 = randi([0 7e5])
a = [0,0];
b = [b1,b2];
c = [c1,c2];
d = [d1,d2];
e = [e1,e2];
% straight line function from a to b
func1 = @(x)a(2) + (a(2)-b(2))/(a(1)-b(1))*(x-a(1));
% straight line function from b to c
func2 = @(x)b(2) + (b(2)-c(2))/(b(1)-c(1))*(x-b(1));
% straight line function from c to d
func3 = @(x)c(2) + (c(2)-d(2))/(c(1)-d(1))*(x-c(1));
% straight line function from d to e
func4 = @(x)d(2) + (d(2)-e(2))/(d(1)-e(1))*(x-d(1));
% determine the x values
x1 = linspace(a(1),b(1),20);
x2 = linspace(b(1),c(1),20);
x3 = linspace(c(1),d(1),20);
x4 = linspace(d(1),e(1),20);
% determine the y values
y1 = func1(x1);
y2 = func2(x2);
y3 = func3(x3);
y4 = func4(x4);
% create the figure
figure;
% get a handle to a plot graphics object
hPlot = plot(NaN,NaN,'ro');
% set the axes limits
% iterate through each point on line
for k=1:length(y1)
% update the plot graphics object with the next position
set(hPlot,'XData',x1(k),'YData',y1(k));
% set dotted line
hold on
plot([x1(1), x1(k)], [y1(1), y1(k)], '--k')
xlim([min(0) max(8e5)]);
ylim([min(0) max(8e5)]);
hold off
% pause for 0.1 seconds
pause(0.1);
end
for k=1:length(y2)
% update the plot graphics object with the next position
set(hPlot,'XData',x2(k),'YData',y2(k));
% set dotted line
hold on
plot([x2(1), x2(k)], [y2(1), y2(k)], '--k')
xlim([min(0) max(8e5)]);
ylim([min(0) max(8e5)]);
hold off
% pause for 0.1 seconds
pause(0.1);
end
for k=1:length(y3)
% update the plot graphics object with the next position
set(hPlot,'XData',x3(k),'YData',y3(k));
% set dotted line
hold on
plot([x3(1), x3(k)], [y3(1), y3(k)], '--k')
xlim([min(0) max(8e5)]);
ylim([min(0) max(8e5)]);
hold off
% pause for 0.1 seconds
pause(0.1);
end
for k=1:length(y4)
% update the plot graphics object with the next position
set(hPlot,'XData',x4(k),'YData',y4(k));
% set dotted line
hold on
plot([x4(1), x4(k)], [y4(1), y4(k)], '--k')
xlim([min(0) max(8e5)]);
ylim([min(0) max(8e5)]);
hold off
% pause for 0.1 seconds
pause(0.1);
end

I'm looking for a way which will allow me to input a target value, say 8e5, and the line will start plotting to that point in a given number steps and each step there is a percentage chance that a new target will be generated and the point will change direction and start moving to the new target which would then repeat a given number of times.

Is this possible?

Thanks

Answer 1

[Paul Hoffrichter]

Not sure exactly what you want, but possibly this is getting close. The refactoring should make it easier to modify.

% set randomizer for repeatability; comment out if repeatability not wanted
rng(12345);

%% Inputs:
tgt = 8e5;
changeTgtPercent = 12; % percent (2-100%)
numberTimesToRepeat = 20;

%% create the figure
figure;
hPlot = plot(NaN,NaN,'ro'); % get a handle to a plot graphics object
% set the axes limits
xlim([min(0) max(tgt)]);
ylim([min(0) max(tgt)]);
title(['Change Tgt: ' num2str(changeTgtPercent) '%']);


%% determine the x and y values
pt1 = [0,0];
[xx, yy, lastPt] = selectPath(pt1);
[lastPt, tgt] = movePoint(hPlot, xx, yy, changeTgtPercent, tgt);

while numberTimesToRepeat > 0
   [xx, yy, lastPt] = selectPath(lastPt); % determine the x and y values
   [lastPt, tgt] = movePoint(hPlot, xx, yy, changeTgtPercent, tgt);
   numberTimesToRepeat = numberTimesToRepeat - 1;
end % END Wwhile


%% select a path for the next line
function [xx,yy, lastPt] = selectPath(pt1)
   lastPt = [randi([0 7e5]), randi([0 7e5])]; % not sure if you still want this
   % determine the xx and yy
   xx = linspace(pt1(1),lastPt(1), 20);
   func2 = @(x) lastPt(2) + (lastPt(2)-pt1(2))/(lastPt(1)-pt1(1))*(x-lastPt(1)); % straight line to lastPt
   yy = func2(xx);
end

%% Draw the moving points
function [lastPoint, newTgt] = movePoint(hpl, xx, yy, changeTgtPercent, tgt)
   numPts = length(yy);
   rndVal = randi([2 100]);
   if rndVal <= min( changeTgtPercent, numPts )
      numPts = rndVal;
      newTgt = randi([6.5e5 7e5]);  % change the target here
   else
      numPts = length(yy);
      newTgt = tgt;
   end
   for k=1:numPts
      % update the plot graphics object with the next position
      set(hpl,'XData',xx(k),'YData',yy(k));
      % set dotted line
      hold on
      plot([xx(1), xx(k)], [yy(1), yy(k)], '--k')
      hold off
      pause(0.02);
   end
   lastPoint = [xx(k), yy(k)];
end

[Jack Rimmer]

Apologies if I didnt make that clear, but that looks to be exactly what I'm looking for.

However I'm getting an error of:

Unrecognized function or variable 'selectPath'.

Is that command from a specific add on or module?

[Paul Hoffrichter]

>> Is that command from a specific add on or module?

No, I made up that function. selectPath is a local function defined in the post. There is also another local function in the post, movePoint

I am using MATLAB R2020a. What version are you using? Did you hit the Copy button on the top right corner of my post and paste into MATLAB without changing any lines?

Maybe you can cut the selectPath code and put it into another file, called selectPath.m

And also create another file named movePoint.m by cutting its code likewise.

In general, have you ever had any luck defining local functions in a script before? If so, then do a "find" and search for selectPath to make sure there is not a typo.

[Jack Rimmer]

I'm on version R2020b, copied the code straight in nothing changed.

>> find selectPath

ans =

     1     2     3     4     5     6     7     8     9    10

>> find movePoint

ans =

     1     2     3     4     5     6     7     8     9

I've defined variables in this way before, but for whatever reason, this one isn't working

[Paul Hoffrichter]

What you are doing with find is just counting chars.

>> find abcxyz
ans =
     1     2     3     4     5     6

You should just run the script directly. You should not try to call selectPath from the command line.

Since you copied the text to MATLAB without making changes, then either your version is broken, or you are not running the program correctly. In either case, by contacting MathWorks, you should be able to resolve the problem.

https://www.mathworks.com/support/contact_us.html?s_tid=hp_ff_s_support

Answer 2

[Paul Hoffrichter]

You should just run the script directly. You should not try to call selectPath from the command line.

[Jack Rimmer]

Yep that did the trick, thanks a lot for all your help!

Answer 3

[Steven Lord]

Rather than creating a large number of small line segments, you may want to look at either the animatedline function (and the addpoints function associated with the lines returned by animatedline) or maybe the comet function.