Calculate area of a data set

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Dear all,

I have to find the area to the left and right of a x limit which is defined as the x corresponding to the y minimum. I join you my data set. I've used the function convhull to approximate my data. Now I need to find the area, I've tried with the trapz function but it doesn't work. And I'm not sure if it work well in both positive and negative part... Here is my code :

mat = load('hand dual.txt');
X = -mat(:,1);
%Y = mat(:,2);
Z = -mat(:,3);
hull = convhull(X,Z);
figure(1) 
plot(X(hull),Z(hull));
figure(2)
plot(X,Z);
min_val = min(Z(hull));
max_val = max(Z(hull));
ind_limit_X = find(Z(hull)==min_val);
%ind_max_Y = find(Z(hull)==max_val);
new_X = X(hull);
new_Y = Z(hull);
left_X = [];
right_X = [];
X_limit = new_X(ind_limit_X);
for i=1:length(new_X)
      if (new_X(i) <= X_limit)
          left_X(end+1) = new_X(i);
          Y_corresponding = new_Y(i);
          left_area =
  trapz(left_X(1:length(left_X)),Y_corresponding(1:length(left_X)));
      end
      if (new_X(i) >= X_limit)
          right_X(end+1) = new_X(i);
          Y_corresponding2 = new_Y(i);
          right_area = trapz(right_X(1:length(right_X)),Y_corresponding2(1:length(right_X)));
      end
  end

I've the following error :

Error using permute
ORDER contains an invalid permutation index.
Error in trapz (line 43)
  y = permute(y,perm);
Error in hand_pos (line 24)
        left_area = trapz(left_X(1:length(left_X)),Y_corresponding(1:length(left_X)));