I am trying to plot the each value of C at different theta values, but I found an error. Error: Invalid expression. When calling a function or indexing a variable, use parenth

clear all

clc

c=[0.5,0.75,1,1.1];

theta=[-pi:0.01:pi];

a=zeros(1,629);

for k=c

G(k)=(1+4*(a(k)).^2-a(k)).*(sin(theta/2)).^2);

plot(G(k),theta);

end

[Dyuman Joshi]

Your syntax is incorrect. You are using k as an index, a(k), which must be a natural number. Values in c are not natural numbers.

c=[0.5,0.75,1,1.1];
theta=[-pi:0.01:pi];
a=zeros(1,629);
for k=c
     %^
    G(k)=(1+4*(a(k)).^2-a(k)).*(sin(theta/2)).^2);
    plot(G(k),theta);
end

Also, if all the values of a are zero, you will get the same graph repetedly.

[Seifeldin Mohamed]

Cs are required values!! , so which statment should be edite to be able to count for float numbes !!

[Walter Roberson]

Are you trying to define G as being a piecewise formula? Or is G to be a matrix of values? Matrices need to be indexed with positive integers.

Answer 1

[Walter Roberson]

you have too many ) on that line.

Answer 2

[Alan Stevens]

Do you want something more along the following lines?

c=[0.5,0.75,1,1.1];
theta=-pi:0.01:pi;
%a=zeros(1,629);
for k=1:numel(c)  % numel is number of elements in c
    % There are four values of c and all the a's are zero
    % so I've replaced a by c in the following.
    G(k,:)=(1+4*c(k).^2-c(k)).*sin(theta/2).^2;
    
end
plot(theta,G);
xlabel('\theta'), ylabel('G')