Plot Error Please help

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Ryan Williams
Ryan Williams el 14 de Mzo. de 2021
Comentada: Star Strider el 14 de Mzo. de 2021
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)

Respuesta aceptada

Star Strider
Star Strider el 14 de Mzo. de 2021
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.
  2 comentarios
Ryan Williams
Ryan Williams el 14 de Mzo. de 2021
Thank you!
Star Strider
Star Strider el 14 de Mzo. de 2021
As always, my pleasure!

Iniciar sesión para comentar.

Más respuestas (1)

KALYAN ACHARJYA
KALYAN ACHARJYA el 14 de Mzo. de 2021
Editada: KALYAN ACHARJYA el 14 de Mzo. de 2021
There must be one else condition (to avoid any mismatch between vectors length). If none of the conditions is true, then such condition y will be the "else" condition. Sure, some cases theta(i) maynot be satisfy any of those conditions.
Pre-allocation also helps to avoid a mismatch between the lengths of the vectors, but whether this is true in the case of your condition, if a theta (i) if-and, is not part of the conditions, then y should be zero .
Or assign last one as an "else" condition (Check the coditions)
theta = linspace(0,2*pi,500);
y=zeros(1,numel(theta)); % Thise also helps to avoid mismatch between vectors length
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;
else
%(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)

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