Area between a curve and a baseline

Question

Joe Abraham 2012-11-13

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/53554-area-between-a-curve-and-a-baseline

I want to create a base line (red line) from the plot and calculate area between the base line and curve (blue line).Curve is a vector. Baseline is drawn manually using code below. [x y]=ginput(2); line(x,y);

Any help/ suggestions is highly appreciated.

Thanks

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Andrei Bobrov 2012-11-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/53554-area-between-a-curve-and-a-baseline#answer_65174

编辑：Andrei Bobrov 2012-11-13

在 MATLAB Online 中打开

data - your array < 2 x N >, data(1,:) - abscissa; data(2,:) - ordinate.

plot(data(1,:),data(2,:));
[x y]=ginput(2);
t = x(1) <= data(1,:) & x(2) >= data(1,:);
X = data(1,t);
out = trapz(X,diff([interp1(x,y,X);data(2,t);]))

3 个评论
显示 1更早的评论隐藏 1更早的评论

Andrei Bobrov 2012-11-13

corrected

Joe Abraham 2012-11-28

Sorry for delayed reply. I got the following error when computed ur code.

??? Attempted to access xx(:,1); index out of bounds because size(xx)=[3,0].

Error in ==> specgraph.areaseries.refresh at 82 v = [xx(:,k) yy(:,k)];

Error in ==> graph2d.series.schema>LdoDirtyAction at 108 refresh(h);

Warning: Error occurred while evaluating listener callback. > In area at 100 In DSC at 27

请先登录，再进行评论。

Answer 2

Teja Muppirala 2012-11-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/53554-area-between-a-curve-and-a-baseline#answer_65176

在 MATLAB Online 中打开

You could try something along the lines of this:

% Just making some data  
x0 = 0:0.001:5;
y0 = sin(x0);
plot(x0,y0);
grid on; set(gca,'layer','top');
% Get your two points
[x y]=ginput(2); line(x,y);
% Break up the line segment into a sufficiently fine grid
N = 10001; 
x_fine = linspace(x(1),x(2),N);
dx = x_fine(2)-x_fine(1);
% Interpolate the values at the grid points 
top = interp1(x0,y0,x_fine); % Top of the area
bottom = interp1(x,y,x_fine); % Bottom of the area
% Get the area using TRAPZ and show it
area = dx*trapz(top-bottom)
patch([x_fine fliplr(x_fine)], [top fliplr(bottom)],'r');

Just replace the sine with whatever data you are using (the example above uses row vectors, so if your data is in a column instead, you'll probably have to make some minor modifications)