refactor to minimize code plot size.

Added code to set x,y labels and title, and to set xlim, ylim
in one line.

Also moved some plotting code to the *internal.py files.

code/nonlinear_internal.py

@@ -0,0 +1,50 @@
+# -*- coding: utf-8 -*-
+"""
+Created on Thu Jul  9 13:02:32 2015
+
+@author: Roger Labbe
+"""
+
+import filterpy.stats as stats
+import matplotlib.pyplot as plt
+from matplotlib.patches import Ellipse
+import numpy as np
+
+
+def plot1():
+
+    stats.plot_covariance_ellipse((10, 2), P, facecolor='g', alpha=0.2)
+
+
+def plot2():
+    P = np.array([[6, 2.5], [2.5, .6]])
+    circle1=plt.Circle((10,0),3,color='#004080',fill=False,linewidth=4, alpha=.7)
+    ax = plt.gca()
+    ax.add_artist(circle1)
+    plt.xlim(0,10)
+    plt.ylim(0,3)
+    P = np.array([[6, 2.5], [2.5, .6]])
+    stats.plot_covariance_ellipse((10, 2), P, facecolor='g', alpha=0.2)
+
+def plot3():
+    P = np.array([[6, 2.5], [2.5, .6]])
+    circle1=plt.Circle((10,0),3,color='#004080',fill=False,linewidth=4, alpha=.7)
+    ax = plt.gca()
+    ax.add_artist(circle1)
+    plt.xlim(0,10)
+    plt.ylim(0,3)
+    plt.axhline(3, ls='--')
+    stats.plot_covariance_ellipse((10, 2), P,  facecolor='g', alpha=0.2)
+
+def plot4():
+    P = np.array([[6, 2.5], [2.5, .6]])
+    circle1=plt.Circle((10,0),3,color='#004080',fill=False,linewidth=4, alpha=.7)
+    ax = plt.gca()
+    ax.add_artist(circle1)
+    plt.xlim(0,10)
+    plt.ylim(0,3)
+    plt.axhline(3, ls='--')
+    stats.plot_covariance_ellipse((10, 2), P,  facecolor='g', alpha=0.2)
+    plt.scatter([11.4], [2.65],s=200)
+    plt.scatter([12], [3], c='r', s=200)
+    plt.show()