MATLAB: Need help getting the points to move separately.

functiongaussianvelocity

Attached are a script and a function file. For the script if I run it before doing the steps it'll have 20 points in different places, but after I put in the velocities they all converge, any idea on how to get each point to move separately. I need all of the velocities to be rand which is why I created a function to do a random velocity based on gaussian distribution.

Best Answer

% Do this one, insert x, y, z, within for loop

    % Modification 
  for i=1:20
    x=r.*sin(theta).*cos(phi);
    y=r.*sin(theta).*sin(phi);
    z=r.*cos(theta);
    x(i+1)=x(i)+velocities_fun(x)*dt;
    y(i+1)=y(i)+velocities_fun(y)*dt;
    z(i+1)=y(i)+velocities_fun(z)*dt;
end

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I guess, the problem is that you overwrite x, y and z in each iteration:

x = zeros(length(t),1);
y = zeros(length(t),1);
z = zeros(length(t),1);
for i=1:length(t)-1
   x=r.*sin(theta).*cos(phi);   % Here x is overwritten by a 20x1 vector!
   y=r.*sin(theta).*sin(phi);
   z=r.*cos(theta);
   x(i+1)=x(i)+velocities_fun(x)*dt;  % This fails for i=21
   y(i+1)=y(i)+velocities_fun(y)*dt;
   z(i+1)=y(i)+velocities_fun(z)*dt;
end

Use another variable:

x = zeros(length(t),1);
y = zeros(length(t),1);
z = zeros(length(t),1);
% This does not depend on the loop counter, so move it before the loop:
xc = r .* sin(theta) .* cos(phi);
yc = r .* sin(theta) .* sin(phi);
zc = r .* cos(theta);
for i = 1:length(t)-1
   x(i+1) = x(i) + velocities_fun(xc) * dt;
   y(i+1) = y(i) + velocities_fun(yc) * dt;
   z(i+1) = y(i) + velocities_fun(zc) * dt;
end

Do you see, that some spaces around the operators improve the readability?

By the way: You use the first output of velocities_fun only, and no inputs. So you can simplify it to:

function V = velocities_fun()
V = normrnd(1,1);
end

But then creating xc, yc, zc is not useful at all.

MATLAB: Antenna array pattern in 3D space

Hi Tadej, In this for loop

for I=1:N
    R=An(I)*exp(1j.*(Ep+Jp(I)));
    Ep=B*((Xn(I).*cos(PHI).*sin(THETA))+(Yn(I).*sin(THETA).*sin(PHI))+(Zn(I).*cos(THETA)));
end

You attempt to access the value of Ep the first time through the loop before it has been assigned a value. Perhaps you just need to swap the two lines and place the Ep= assignment before the R=

Also, do you know about the new Phased Array System Toolbox? That toolbox will greatly enhance your ability to design antennas and model phased array systems.

Wayne

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