Plotting a parametric curve in Matlab..(Dimension error)

Hey all, i'm trying to plot the contours of constant e=0, 0.1, 0.2, 0.3 and 0.4 using the parametric expression of

x=e*cos(theta)/sqrt(4/3+4/3*cos(theta)*sin(theta) , y=e*sin(theta)/sqrt(4/3+4/3*cos(theta)*sin(theta))

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I tried it like this, but got errors on dimension.

When i tried on ,for example, e=0.1 case,

theta=0:0.1:(2*pi);

e=0.1;

x=e*cos(theta)/sqrt(4/3+4/3*cos(theta)*sin(theta));

y=e*sin(theta)/sqrt(4/3+4/3*cos(theta)*sin(theta));

plot(x,y)

then, i got error message about dimension errors in matrix multiplication. Could you help me on this ?

and my last question is, Is there a way to change only the e-values and show them all in one picture?

Thank you

Answer 1

[Star Strider]

Use element-wise operations (the ‘dot operator’):

x=e*cos(theta)./sqrt(4/3+4/3*cos(theta).*sin(theta));
y=e*sin(theta)./sqrt(4/3+4/3*cos(theta).*sin(theta));

That worked when I ran it.

EDIT —

You can plot them all at the same time (without loops) by using matrix operations as well as element-wise (array) operations:

theta=0:0.1:(2*pi);
e=[0.1; 0.2; 0.3; 0.4];
x=e*cos(theta)./sqrt(4/3+4/3*cos(theta).*sin(theta));
y=e*sin(theta)./sqrt(4/3+4/3*cos(theta).*sin(theta));
plot(x.',y.')

.