How do I plot my function that I made? It's piecewise.

I need to plot this graph on the interval (-2,20), I'm also supposed to use a for loop to plot but I don't know how.

function y = y(t)   
    if (t < 0)
        y = -9;
 
    elseif ((0 <= t)&& (t < 10))
        y  = -9*cos(3*t);
 
    elseif (t >= 10)
        y = -9*cos(3*t)*(exp(-0.1*(t-10)));
    end
end

Thanks a lot

[Stephen23]

Forget about IF, you should vectorize your code using logical indexing:

https://www.mathworks.com/help/matlab/matlab_prog/vectorization.html

Answer 1

[madhan ravi]

Try this:

% Logical indexing is the way I would do it but since you requested
t=-2:.001:20;
plot(t,Y(t))
%      ^^^^---function call

function y = Y(t) %function definition
y = zeros(size(t)); % pre-allocate
for k=1:numel(t)
    if (t(k) < 0)
        y(k) = -9;
        
    elseif ((t(k) >= 0)) && (t(k) < 10)
        y(k)  = -9*cos(3*t(k));
        
    elseif (t(k) >= 10)
        y(k) = -9*cos(3*t(k))*(exp(-0.1*(t(k)-10)));
    end
end
end

Answer 2

[Star Strider]

I generally use Anonymous Functions (link) for these problems:

y = @(t) -9*(t < 0) + (-9*cos(3*t)).*((0 <= t) & (t < 10)) + (-9*cos(3*t).*(exp(-0.1*(t-10)))).*(t >= 10);

t = linspace(-5, 75, 500);

figure
plot(t, y(t))
grid

Note that ‘short circuit’ (duplicate) operators, such as ‘&&’ and ‘||’ only work for logical scalars, not logical vectors.