How can I calculate the area between two curves in a specific section?

I have two curves which have several intersection points (see attachment). I want to calculate the green filled area in between two intersection points. It works to calculate and display the intersection points. However I am struggling to calculate just this specific (green filled) area with the trapz function since there always pops up following error message:

"Index in position 1 is invalid. Array indices must be positive integers or logical values."

[xj,yj] = polyxpoly(x,y1,x,y2); %calculate intersection points %y1 straight line %y2 mean

mapshow(xj,yj,'DisplayType','point','Marker','o');%show intersection points

A=[xj,yj];

for n=length(xj):-1:1

k=A(n,:);

k(:,2)=[];

l=A(n-1,:);

l(:,2)=[];

isec1= find(y2==l);

isec2= find(y2==k);

a = trapz(isec1:isec2,y1(isec1:isec2,1))-trapz(isec1:isec2 ,y2(isec1:isec2,1));

end

Answer 1

[Priyanshu Mishra]

Hi Daniel,

When n=1, n-1 goes to zero for which A(0,:) is an invalid index. The error you are getting is becuse of this only.

[daniel ordnung]

perfect thank you!