How to plot contour?

Have 3 random variables, but need to plot in two dimensions.

Here is the function.

f=1+2*r1*cos(omega)+2*r2*cos(2*omega).
X axis: r1    [-1,1]
Y axis: r2    [-1,1]

Plot the contour which makes f>=0 for all omegas. In other words, plot the contour which makes the minimum value of f is 0.

Apparently, (-0.5,0), (0.5,0), (0,0.5), (0,-0.5) are four points on the contour.

Thanks in advance.

[Walter Roberson]

You are only plotting against r1 and r2: since f>=0 for all omega there is no point plotting the values of omega, just whether f>=0 for all (r1,r2,:) locations.

[Xu]

Yes, you are absolutely right. That's what I asked. I said "plot in two dimensions r1 for x axis and r2 for y axis".

I need to find (r1, r2) which can make fmin=0;

For example, for (r1, r2)=(0.5, 0), f=1+cos(omega), fmin=0 obviously.

[Walter Roberson]

hints:

ndgrid()

bsxfun()

all()

contour()