How to shade and calculate area above a reference line in a plot?

Hello,

In the attached plot, I want to shade the area ONLY ABOVE the 0-crossing line without losing the curve below the 0-line.

I also want to calculate the area above the 0-crossing line.

I searched the community for answers and found several solutions to similar questions but it was not specific to this issue.

Could someone please help me? I would very much appreciate a code snippet to help solve this issue.

Thank you.

Answer 1

[Robert U]

Hi Bhaskar Ravishankar,

You can use area and logical indexing in order to shade the curve:

resX = 0.1;
xlim = [-pi,pi];

x = xlim(1):resX:xlim(2);
y = 1 * sin( x );

fh = figure;
ah = axes(fh);
hold(ah,'on');
ah.XGrid = 'on';
ah.XMinorGrid = 'on';
ah.YGrid = 'on';
ah.YMinorGrid = 'on';


plot(ah,x,y,'-black');
area(ah,x(y>=0),y(y>=0)); % in order to suppress the visual uncertainties you would have to split the area, or make sure to hit the zero crossings.

Integral of the area with non-negative values:

intArea = sum(y(y>=0)*resX);

Kind regards,

Robert

[Bhaskar Ravishankar]

Hi Robert,

I tried this technique with my code and I saw that the -ve portion of my graph disappears when I use area the area command. I'm not able to figure out why. Any suggestions?

I used the 'hold on' command after I plotted the graph before the area command but it gave me completely different results. Not sure what happened there.

The x limits were the same. But it didn't work.

[Robert U]

Probably, you have not enough data points available. Try to remesh your xdata, interpolate the y-data using linear interpolation and then use area command on your interpolated data.

If you want more than generic help, post your code and data.

Kind regards,

Robert