MATLAB: Plot Error Please help

plotplotting

I'm trying to plot a piecewise function that I've created and it keeps giving me an error saying "vectors must be same length." this is what I have. Please help.
theta = linspace(0,2*pi,500);
for i=1:numel(theta)
    if (theta(i) >= 0) && (theta(i) <= (pi/2))
        y(i) = 6*(2*theta(i) - 0.5*sin(theta(i)));
    elseif (theta(i) >= (pi/2)) && (theta(i) <= (2*pi/3))
        y(i) = 6;
    elseif (theta(i) >= (2*pi/3)) && (theta(i) <= (4*pi/3))
        y(i) = 6 - 3*(1 - 0.5*cos(3*theta(i) - 2*pi));
    elseif (theta(i) >= (4*pi/3)) && (theta(i) <= (3*pi/2))
        y(i) = 3;
    elseif (theta(i) >= (3*pi/2)) && (theta(i) <= (7*pi/4))
        y(i) = 3 - 1.5*((theta(i) - (3*pi/2))/(pi/4))^2;
    elseif (theta(i) >= (2*pi/3)) && (theta(i) <= (4*pi/3))
        y(i) = 0.75 - 0.75*(1 - (theta(i) -(7*pi/4))/(pi/4))^2;
    end
end
plot(theta,y,'r','linewidth',2)

Best Answer

It’s necessary to account for absolutely all possibilities.
Try this: 
theta = linspace(0,2*pi,500);
for i=1:numel(theta)
    if (theta(i) >= 0) && (theta(i) < (pi/2))
        y(i) = 6*(2*theta(i) - 0.5*sin(theta(i)));
    elseif (theta(i) >= (pi/2)) && (theta(i) < (2*pi/3))
        y(i) = 6;
    elseif (theta(i) >= (2*pi/3)) && (theta(i) < (4*pi/3))
        y(i) = 6 - 3*(1 - 0.5*cos(3*theta(i) - 2*pi));
    elseif (theta(i) >= (4*pi/3)) && (theta(i) < (3*pi/2))
        y(i) = 3;
    elseif (theta(i) >= (3*pi/2)) && (theta(i) < (7*pi/4))
        y(i) = 3 - 1.5*((theta(i) - (3*pi/2))/(pi/4))^2;
    elseif (theta(i) >= (2*pi/3)) && (theta(i) <= (4*pi/3))
        y(i) = 0.75 - 0.75*(1 - (theta(i) -(7*pi/4))/(pi/4))^2;
    else                                                                % Added Condition
        y(i) = 0;                                                       % Added Assignment
    end
end
figure
plot(theta,y,'r','linewidth',2)
That ran without error when I tested it.
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