Add program to graph theoretical vs experimental COBS/R overhead

I wrote this a long time ago, but didn't put it into version control
until now.

Author: cmcqueen

doc/pyplots/cobsr_overhead.py

@@ -0,0 +1,59 @@
+
+from matplotlib import pyplot as plt
+import numpy as np
+from cobs import cobs
+from cobs import cobsr
+
+
+def cobsr_overhead_calc(num_bytes):
+    return 257./256 - (255./256)**num_bytes
+
+def cobsr_overhead_measure(num_bytes):
+    # TODO: review value
+    NUM_TESTS = 10000
+    overhead = 0
+    for _i in xrange(NUM_TESTS):
+        output = cobsr.encode(np.random.bytes(num_bytes))
+        overhead += (len(output) - num_bytes)
+    return overhead / float(NUM_TESTS)
+
+def cobs_overhead_measure(num_bytes):
+    # TODO: review value
+    NUM_TESTS = 10000
+    overhead = 0
+    for _i in xrange(NUM_TESTS):
+        output = cobs.encode(np.random.bytes(num_bytes))
+        overhead += (len(output) - num_bytes)
+    return overhead / float(NUM_TESTS)
+
+fig = plt.figure()
+ax1 = fig.add_subplot(111)
+
+# x-range for plot
+num_bytes_list = np.arange(1, 30)
+
+# Calculate values and plot
+
+# Measured values for COBS
+#cobs_measured_overhead = [ cobs_overhead_measure(num_bytes) for num_bytes in num_bytes_list ]
+#ax1.plot(num_bytes_list, cobs_measured_overhead, 'g.')
+
+# Measured values for COBS/R
+cobsr_measured_overhead = [ cobsr_overhead_measure(num_bytes) for num_bytes in num_bytes_list ]
+ax1.plot(num_bytes_list, cobsr_measured_overhead, 'r.')
+
+# Calculated values for COBS/R
+cobsr_calc_overhead = [ cobsr_overhead_calc(num_bytes) for num_bytes in num_bytes_list ]
+ax1.plot(num_bytes_list, cobsr_calc_overhead, 'b.')
+
+ax1.set_xlabel('message length (bytes)')
+ax1.set_xlim(min(num_bytes_list), max(num_bytes_list))
+
+# Make the y-axis label and tick labels match the line color.
+ax1.set_ylabel('encoding overhead (bytes)')
+if 0:
+    ax1.set_ylabel('encoding overhead (bytes)', color='b')
+    for tl in ax1.get_yticklabels():
+        tl.set_color('b')
+
+plt.show()