Index exceeds the number of array elements (10).

Having troubble with the last loop (it runs fine without it) i know its not the most elegent code but im pretty new to this. please explain like im 4 years old*

clear;
x=[1 2 3.25 4.5 6 7 8 9 9.5 10];
y=[5 6 5.5 7 8.5 8 6 7 7 5];
plot(x,y);
n=length(x);


for i=1:n-1
   line([x(i) x(i)],[0 y(i)]);
   
end
A=zeros(1,n-1);
Area=0;
for i=1:2 & 4:5
    A(i)=0.5*(x(i+1)-x(i))*(y(i+1)+y(i));
    Area=Area+A(i);
end
for i=2:4 & 8:10
    A(i)=(x(i+2)-x(i))*((y(i)+4*y(i+1)+y(i+2))/6); 
    Area=Area+A(i);
end
for i=5:8
    A(i)=(x(i+3)-x(i))*((y(i)+3*y(i+1)+3*y(i+2)+y(i+3))/8); 
    Area=Area+A(i);
end

Answer 1

[Star Strider]

In this line:

A(i)=(x(i+3)-x(i))*((y(i)+3*y(i+1)+3*y(i+2)+y(i+3))/8); 
                                                ↑ ← HERE

when ‘i’ is 8, addresses ‘y(11)’ when ‘y’ has only 10 elements.

[Nick mardero]

so how would i fix this?

[Star Strider]

The easiest way:

for i=5:7  ← STOP AT 7
    A(i)=(x(i+3)-x(i))*((y(i)+3*y(i+1)+3*y(i+2)+y(i+3))/8); 
    Area=Area+A(i);
end

Of course an even easier way would be:

A = cumtrapz(x,y)

although you’re likely not allowed to do that.