How to color an area at plot surface...

How can i color the area between 2 functions like

f(x)=x^2

g(x)=-x^2+1

Answer 1

[Thomas]

I found a better way... try

 x=1:10;
 f=x.^2;
 g=x.^2+1;
 patch([x x(end:-1:1)], [f g(end:-1:1)],'y')

This sets up x=1...10, g=x² and f=x²+1 and then plots the area between the curves as a yellow polygon/patch. Compare the matlab help for patch.

Here i simply draw all points forf first in positive x direction and then jump to the last point of g and draw the points of g backwards from x=10...1. All in all a complete polygon. Btw, 'y' is the color yellow.

[Masoud Ghanbari]

Hi

It worked but i cant understand the code

for example what if we want to color the area like f-g<2 ???

[Thomas]

i dont understand what you mean by f-g<2. You have to e.g. put the vector with the upper border curve values in f and the lower border data into g (or the other way round, it doesnt matter) and then call the patch command.

[Masoud Ghanbari]

Thanks... Hope to support me at my further problems

Answer 2

[Thomas]

You could use sth like

area(g); 
hold on;
area(f);

and then select f's fill color to be the backgroud color.

Of coures this only works as long as f<g for all x.

If this is not the case you could first do

upperCurve = max(f,g)
lowerCurve = min(f,g)

and then plot upperCurve and lowerCurve as stated above. If they are sufficiently high-res compared to your plot resolution it might be sufficient, however it wouldn't be "clean". Maybe there is another solution anyone can bring up...

Answer 3

[Masoud Ghanbari]

hi

It does not works

would you please bring me the full code

Answer 4

[Muruganandham Subramanian]

hi,

for e,g.

x=[1 2 3 4 5];
   for i=1:numel(x)
  f(i)=x(i)^2;
  g(i)=-x(i)^2+1;
   end
  plot(x,f,x,g)
  hold on;
  area(f-g)
  hold on;
  area(g-f)

Do you expecting like this?