plot a function that has a variable that changes with time

The function has a variable ap that changes at t >= 100s. How do I plot that?

close all; clear; clc
tspan = [0 150];
x0 = [1];
t = linspace(0,150);

bp = 2; am = -1; bm = 1; r = 0.5; gamma = 2;

theta2 = func(t,am,bp)

plot(t,theta2)
function theta2 = func(t,am,bp)

if t >= 100
    ap = 2;    
else
    ap = 1;    
end

theta2 = (am-ap)/bp;
end

Answer 1

[Chien-Han Su]

In your block of 'func', watch out that the 1st input argument 't' might be and indeed a vector in your case through

t = linspace(0,150);

This leads to an ambiguous result , in the 'func', for the if condition

if t >= 100

By typing in the command window

linspace(0,150) >= 100

you can see explicitly that the result is a vector not a single boolean value.

Hence, I suggest you modify the 'func' block by explicitly assign the size of output 'theta2' according to the input 't' and compute elements of the result using a loop. Namely, revise the code into

close all; clear; clc
tspan = [0 150];
x0 = [1];
t = linspace(0,150);
bp = 2; am = -1; bm = 1; r = 0.5; gamma = 2;
theta2 = func(t,am,bp);
plot(t,theta2,'LineWidth',1)
axis([-inf inf -2 -0.5]);
function theta2 = func(t,am,bp)
    numInput = numel(t);
    theta2 = zeros(size(t));
    for i = 1:numInput
        if t(i) >= 100
            ap = 2;    
        else
            ap = 1;    
        end
        theta2(i) = (am-ap)/bp;
    end 
end

The result is shown as follows

Edit: fix typos