Keep getting ERROR: Array indices must be positive integers or logical values for X(t)

I'm trying to write code that plots a graph of an oscillation system and keep getting the "Array indices must be positive integers or logical values." and can't figure out whats going wrong. Any help would be appreciated.

% Matlab Oscillation Assignment
clc; clear;
Vo = 0.6; %initial velocity
del = [0.05 0.1 0.2]; % Damping ratios
Wn = 5; % angular frequency rad/s
t = 0; % initial time
Xo = 0;
while t < 7
    
    Wd = sqrt(1-((del.^2)*(Wn))) %damped angular frequency
    Phase_Angle = atan((del.*Wn.*Xo+Vo)./Wd.*Xo) %phase 
    C = sqrt(Xo.^2+((del.*Wn.*Xo+Vo)./Wd).^2) %amplitude
    X(t) = (C.*exp(1).^-del.*Wn.*t).*cos ((Wd.*t)-Phase_Angle) % equation for response of the system
    t = t+1;
    Xo = X(t);
    grid on
    plot(t,X(t),'-or')
    hold on
    
end

[Stephen23]

You have:

t = 0; % initial time
..
while t < 7
    ..
    X(t) = ..

Is 0 a valid index (i.e. an integer >=1) ?

[Dyuman Joshi]

Numerical indices in MATLAB start from 1, not 0.

As you are using t as a numerical index, it should be a positive integer.

Also, you are trying to assign a 1x3 array (the rhs to X(t)) to a 1x1 element (X(t)), which will give an error.

Since I do not know what you are trying to do, I can not provide you with any suggestions/solutions.

Answer 1

[Star Strider]

Create ‘X’ as an anonymous function:

X = @(t,C,Wd,Phase_Angle) (C.*exp(1).^-del.*Wn.*t).*cos ((Wd.*t)-Phase_Angle) % equation for response of the system

and then call it in the loop —

% Matlab Oscillation Assignment
clc; clear;
Vo = 0.6; %initial velocity
del = [0.05 0.1 0.2]; % Damping ratios
Wn = 5; % angular frequency rad/s
t = 0; % initial time
Xo = 0;
X = @(t,C,Wd,Phase_Angle) (C.*exp(1).^-del.*Wn.*t).*cos ((Wd.*t)-Phase_Angle); % equation for response of the system
while t < 7
    
    Wd = sqrt(1-((del.^2)*(Wn))); %damped angular frequency
    Phase_Angle = atan((del.*Wn.*Xo+Vo)./Wd.*Xo); %phase 
    C = sqrt(Xo.^2+((del.*Wn.*Xo+Vo)./Wd).^2); %amplitude
    t = t+1;
    Xo = X(t,C,Wd,Phase_Angle);
    grid on
    plot(t,Xo,'-or')
    hold on
    
end

This works, however there are obviously still problems. I leave those to you to resolve.

.