How To plot areas like: f(x) > mx +b ???

Hi everyone,

I'm trying to plot functions directly from FPLOT...

For instance:

fplot(@(x)10*x, [-10 10]);

BUT How can i plot "filled" graphs to indicate f(x)>10x or f(x)<10x

Thanks in advance!

Answer 1

[Star Strider]

You can’t do it with fplot but you can with patch:

x  = linspace(0, 10, 2);
f1 = @(p,x) p(1).*x + p(2);
b1 = [0.7  1.0];
fv1 = f1(b1,x);

x1p = [x(1) x(2) x(2) x(1)]';
y1p = [fv1(1) fv1(2) fv1(2) fv1(2)]';

figure(1)
hp = patch(x1p, y1p, [0.1 0.1 0.9]);
axis([0  10    0  max(y1p)])
text(3, 5, '\bff(x) > 0.7 x + 1\rm', 'Color','r')

f2 = @(p,x) p.*x;
b2 = 10;
fv2 = f2(b2,x);

x2p = [x(1) x(2) x(2) x(1)]';
y2p = [fv2(1) fv2(1) fv2(2) fv2(1)]';

figure(2)
hp = patch(x2p, y2p, [0.1 0.9 0.1]);
axis([0  10    0  max(y2p)])
text(5, 20, '\bff(x) < 10 x\rm', 'Color','b')

Note the difference in order between ‘y1p’ and ‘y2p’ to get the ‘greater than’ and ‘less than’ respectively. (The vectors in [brackets] in the patch argument list are colour vectors.) Experiment with patch to appreciate what it can do.

Answer 2

[F]

It worked fine!!

Thaaanks! ;)

[Star Strider]

My pleasure!