I m trying to plot some data with pcolor. The data should be plotted on a ring. Inside and outside of the ring should be white area. However, now I have black area. Where is my mistake? Minimal working example:

from matplotlib import cm
import matplotlib.pyplot as plt
from pylab import *

import numpy as np
import scipy as sp

X = np.arange(-1.0, 1.01, 0.01)
Y = np.arange(-1.0, 1.01, 0.01)
X, Y = np.meshgrid(X, Y)

[r, R] = [0.25, 1.0]
an = sp.linspace(0,2*sp.pi,100)

I m trying to plot some data with pcolor. The data should be plotted on a ring. Inside and outside of the ring should be white area. However, now I have black area. Where is my mistake? Minimal working example:

from matplotlib import cm
import matplotlib.pyplot as plt
from pylab import *

import numpy as np
import scipy as sp

X = np.arange(-1.0, 1.01, 0.01)
Y = np.arange(-1.0, 1.01, 0.01)
X, Y = np.meshgrid(X, Y)

[r, R] = [0.25, 1.0]
an = sp.linspace(0,2*sp.pi,100)