Plot(x,y2) with if condition y1(x)

Hello i've got stuck with some code.

What i want to get is this shape of two functions:

I know y function and how to draw it but i've got problem with y^2 function and its domain.

Here's my code

clc
clear all
close all

dt=0.01;
t=[0:dt:4*pi];

w=1;
A=2;
y1=A.*cos(t).*(sin(2.*w.*t)).^2;
y2=y1.^2

plot(t,y1,'r')
hold on

xlabel('time')
ylabel('Amplitude')
grid on

if y1>0
    plot(t,y2,'og')
end

Sadly, i get only visual of y1 not y2 :(

What should I do using if statement or some other loops?

[Adam Danz]

"I know y function and how to draw it but i've got problem with y^2 function"

What's the problem and what's the goal? Is the green line supposed to be connected with peaks in between?

[Kacper Wybranski]

The y^2 function was supposed to appear only when y function has values over 0, the answer from Fangjun Jiang helped.

Answer 1

[Fangjun Jiang]

You can check the output of y1>0. It's a vector so shouldn't be used in if statement.

what you need for y2 is

index=y1>0
plot(t(index),y2(index),'og')