Plot a parametric curve in MathLab

Hey, I am completely new to MatLab and is at the moment trying to figure out how to plot this curve into MatLab!

r(t) = t cos t i + t sin t j + ((2 * sqrt(2)) / 3) * t3/2 k, where 0 <= t <= 2*pi.

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I tried it like this, but got alot of errors:

">> t = 0 : 2*pi

">> i = t*sin(t) //Gives me error "Using *. Inner matrix dimension must agree."

">> j = t*sin(t) //Same error as above.

">> k = ((2 * sqrt(2)) / (3)) * t3/2 //Error: "Using . Inputs must be a scalar and a square matrix."

">> plot3(i,j,k)

Answer 1

[Star Strider]

You need to do element-wise operations (particularly multiplication) in your code. See Array vs. Matrix Operations for the details.

If I understand your code correctly, this will work:

r = @(t) [t .* cos(t);   t .* sin(t);  ((2 * sqrt(2)) / 3) * t*3/2];
t = linspace(0, 2*pi, 250);
rt = r(t);

figure(1)
plot3(rt(1,:), rt(2,:), rt(3,:))
grid on
xlabel('i')
ylabel('j')
zlabel('k')

Note that the anonymous function ‘r’ creates a (3xN) matrix where the first row corresponds to ‘i’, the second to ‘j’ and the third to ‘k’, so ‘t’ must always be a row vector for the row indexing to work correctly.