Help With For Loops in Plotting Problem

I have written this formula and it works well...

The thing is I need to use For loops for the values of "Zeta" to change. I need to be able to plot four graphs with values 0.2, 0.4, 0.6, 0.8 for Zeta.

Should I use the For loop on the C_t formula? or would it be better for only the value of Zeta to change? Either way I can't seem to make it work. Any suggestions on how to proceed?

Zeta=0.2;
Nat_fr=2.5;                   %Natural Frequency
Beta= sqrt(1-Zeta.^2);
Tan_theta=Beta/Zeta;
theta=atan(Tan_theta);        %Angle in radians
t= linspace(0,15,100);
%% Equation
c_t= 1-(1/(sqrt(1-Zeta.^2))).*(exp(-Zeta.*Nat_fr.*t)).*sin((sqrt(1-Zeta)).*Nat_fr.*t+atan((sqrt(1-Zeta))/Zeta));

%% Plot
plot(t,c_t)

Answer 1

[Raj]

temp=1;
t= linspace(0,15,100);
Nat_fr=2.5;                   %Natural Frequency
for Zeta=0.2:0.2:0.8
    Beta (temp,1)= sqrt(1-Zeta.^2);
    Tan_theta(temp,1)=Beta(temp,1)/Zeta;
    theta(temp,1)=atan(Tan_theta(temp,1));        %Angle in radians
    %% Equation
    c_t= 1-(1/(sqrt(1-Zeta.^2))).*(exp(-Zeta.*Nat_fr.*t)).*sin((sqrt(1-Zeta)).*Nat_fr.*t+atan((sqrt(1-Zeta))/Zeta));
    %% Plot
    plot(t,c_t)
    hold on
    temp=temp+1;
end
legend ('Zeta=0.2','Zeta=0.4','Zeta=0.6','Zeta=0.8');
grid on;

Answer 2

[per isakson]

Either should work.

I prefer to keep plot() outside the loop because of speed. That requires to make c_t a matrix, which in turn requires an interger loop-counter to reference c_t. Thus, something like this

function cssm1()
    Nat_fr=2.5;                   %Natural Frequency
    Zeta = [0.2,0.4,0.6,0.8];
    t = linspace(0,15,100);
    c_t = nan( length(Zeta), length(t) );  % preallocate
    for jj = 1 : length( Zeta )
%       Beta= sqrt(1-Zeta(jj).^2);
%       Tan_theta=Beta/Zeta(jj);
%       theta = atan(Tan_theta);        %Angle in radians
        %% Equation
        c_t(jj,:) = 1-(1/(sqrt(1-Zeta(jj).^2))).*(exp(-Zeta(jj).*Nat_fr.*t)).*sin((sqrt(1-Zeta(jj))).*Nat_fr.*t+atan((sqrt(1-Zeta(jj)))/Zeta(jj)));
    end
    %% Plot
    plot( t, c_t )
end

sqrt(1-Zeta(jj)) is calculated three times in the equation, which is a bit of waste of cpu-cycles. Ok, that's why you calculate Beta.

I put the code in a function to avoid cluttering of my base workspace.