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

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Jack Rimmer
on 30 Jan 2021

Answered: Steven Lord
on 1 Feb 2021

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

##### 0 Comments

### Accepted Answer

Paul Hoffrichter
on 1 Feb 2021

Edited: Paul Hoffrichter
on 1 Feb 2021

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

##### 4 Comments

Paul Hoffrichter
on 1 Feb 2021

Edited: Paul Hoffrichter
on 1 Feb 2021

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

### More Answers (2)

Paul Hoffrichter
on 1 Feb 2021

Steven Lord
on 1 Feb 2021

##### 0 Comments

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