error with plotting graph

a = 13;

c = 17;

k = 2*pi/3;

theta = 0:0.0001:2*pi;

d2b = -(a*(cos(theta)*(c^2 - a^2*sin(theta).^2).^(3/2) + a^3*sin(theta).^4 + a*c^2*cos(theta).^2 - a*c^2*sin(theta).^2))./(c^2 - a^2*sin(theta).^2).^(3/2);

figure(3)

plot (theta, d2b);

this function isnt letting me plot a graph and it comes up with this message below

Error using *

Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To perform

elementwise multiplication, use '.*'.

Answer 1

[Stephan]

Since theta is a vector you need to perform elementwise multiplication:

a = 13;
c = 17;
k = 2*pi/3;
theta = 0:0.0001:2*pi;
d2b = -(a*(cos(theta).*(c^2 - a^2*sin(theta).^2).^(3/2) + a^3.*sin(theta).^4 + a*c^2.*cos(theta).^2 - a*c^2.*sin(theta).^2))./(c^2 - a^2*sin(theta).^2).^(3/2);
figure(3)
plot (theta, d2b);