MATLAB Answers

Index exceeds the number of array elements (10).

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Nick mardero
Nick mardero on 21 Oct 2020
Commented: Star Strider on 21 Oct 2020
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

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Answers (1)

Star Strider
Star Strider on 21 Oct 2020
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.

  2 Comments

Star Strider
Star Strider on 21 Oct 2020
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.

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