Shading an area boundered by a curve

Question

What would be the easiest way to lightly shade (or hatch; or anything to set it different from the rest) an area in a plot(), below a curve y=x^2, for example ?

Answer 1

area(x,y) should do the trick. I'm not sure if that class has a FaceAlpha property though.

EDIT: Unfortunately, the area class doesn't have a FaceAlpha property. But you can work around that and edit the patch directly:

x=0:pi/10:2*pi;
y=x.^2;
H=area(x,y);
h=get(H,'children');
set(h,'FaceAlpha',0.5); %#Tada!

EDIT2: To shade the area above the curve, you could use a second area plot with a white fill. It's kind of a kludge, but it should work. Starting over:

x=0:pi/10:2*pi;
y=x.^2;
y2=max(y)*ones(size(y));
hold on
H1=area(x,y2);
H2=area(x,y);
set(H2,'FaceColor',[1 1 1]);
axis tight

or building on Jason S's solution, use the baseval input to shade above the curve:

x=0:pi/10:2*pi;
y=x.^2;
baseval=max(y);
H=area(x,y,baseval);
h=get(H,'children');
set(h,'FaceAlpha',0.5,'FaceColor',[0 1 0]);
axis tight

Answer 2

A supplemental example to elaborate on Doresoom's post:

x=0:pi/50:2*pi;
y1=x.^2;
y2=10+5*sin(3*x);
baseval1=20;
baseval2=3;
clf;
hold on;
H1=area(x,y1,baseval1);
H2=area(x,y2,baseval2);
hold off;
h=get(H1,'children');
set(h,'FaceAlpha',0.5,'FaceColor',[1 0.5 0]);
  % set color to orange, alpha to 0.5
h=get(H2,'children');
set(h,'FaceAlpha',0.5,'FaceColor',[0.85 1 0.25]);
  % set color to yellow-green, alpha to 0.5

But where do you set the color ?

h is a handle to a patch (a filled in area); if you type get(h) you can see all its properties. The MATLAB docs on patch properties explain these to some degree.

And how for example would you shade an area above the curve with that principle ?

area creates a patch between a base value and a curve. Doesn't look like there's an easy way to create an area between two curves though.

Answer 3

Without messing with children, you can also:

x = 0:pi/10:2*pi;  % from your example
y = x.^2.;    % from your example

H=area(x,y);
set(H(1),'FaceColor','k');
alpha(.5);

Worked for me, it also helped with some legend issues that I was having.

. To kick a dead question