Modelling gas particles; "Attempted to access x(11); index out of bounds because numel(x)=10."

Hi, I am at the begging of trying to module gas particles currently the get a problem

Attempted to access x(11); index out of bounds because numel(x)=10.

Error in gasparticelbasic (line 20) x(i) = x(i)+velocityx*dt;

This is my current code;

figure(1) n = 10; % Number of data points x = 50*rand(n,1)-25; y = 50*rand(n,1)-25;

 velocityx = 10*rand(1);
 velocityy = 10*rand(1);

 dt = 0.2;

 for i = 1:1:50
    subplot (2,1,1)
    plot(x,y,'o');
    axis([-25,25,-25,25]);
    hold on
    pause(dt);
    hold off

    x(i) = x(i)+velocityx*dt;
    y(i) = y(i)+velocityy*dt;
 end

Any help would be great. Thanks

Answer 1

[Sebastian Castro]

I have two thoughts here.

1. You have an out-of-bounds indexing error because you're saying that x(i) = x(i)+velocityx*dt; , thus making the variable reference an index that hasn't yet been created. If you want to do a basic forward integration, shouldn't you try x(i+1)= x(i)+velocityx*dt; ?

This would require you to define an initial velocity x(1) , and for efficiency, to preallocate your x and y vectors with a known size ... for example x = zeros(100,1);

2. Defining the velocities with rand before the loop means that the value of velocityx and velocityy will be the same for every particle and for every iteration.

• If you want each particle to have a constant velocity for the whole duration, try generating 25 random numbers: velocityx = rand(25,1);
• Else, if you want each particle to have a different random velocity at every time step, call the rand function inside the loop so its value changes at each iteration.

- Sebastian

[Alastair Martin]

Thank you very much.