contourf, outside a region

Hi

I am using contourf to plot a contour of a complex function. See the image below. However I would like to fill the outside of the region, the complement of the green region in the image. How can I achieve that?

regards

Uwe Brauer

The code is the following

if true
   x0 = -3;x1 = 3;Nx = 301;y0 = -3;y1 = 3;Ny = 301;
xv= linspace(x0,x1,Nx);
yv= linspace(y0,y1,Ny);
[x,y] = meshgrid(xv,yv);
z = x + i*y;
f1=@(z)[1 - (2/3)*z+(1/6)*z.^2];
f2=@(z)[1+ (1/3)*z];
g2=feval(f1,z);
g1=feval(f2,z);
g=g1./g2;
gmag = abs(g);
contourf(x,y,gmag,[1 1],'b-');
axis([x0,x1,y0,y1]);
axis('square');
grid on;
print -dpng  regionabs.png 
end

[Uwe Brauer]

[SOLVED]

arr, the function I used is wrong, countourf does precisely what it should do.

sorry for the noise

Uwe Brauer

Answer 1

[Robert U]

Hi Uwe,

while Mischa Kim is changing the background color to some RGB triplet value (in this particular case 'yellow') one can use the contourf levels as well:

 lastlvl = 1;
 contourf(x,y,gmag,[0:(lastlvl-1) 0:(lastlvl-1)],'b-');
 hold on
 contourf(x,y,gmag,[lastlvl lastlvl],'b-');
 axis([x0,x1,y0,y1]);
 axis('square');
 grid on;

Parameter 'lastlvl' can be changed in order to see more contour levels.

The advantage of this solution is: the area color outside changes with the chosen colormap accordingly.

Kind regards,

Robert

[Uwe Brauer]

Hi Robert

taht is a nice solution, thank you.

Although I have to admit that my question was wrong since I plotted the wrong function it is very useful to know your trick, since I might need it in the future.

thanks

Uwe