Update Variance_PURE.py

Author: hharcolezi

multi_freq_ldpy/pure_frequency_oracles/Variance_PURE.py

@@ -1,5 +1,16 @@
 
+# [1] Wang et al (2017) "Locally differentially private protocols for frequency estimation" (USENIX Security 17).
 
 def VAR_Pure(p, q, n=1, f=0):
 
+    """
+    Variance value of 'pure' frequency oracles from [1]
+
+    :param p: probability of being 'honest';
+    :param q: probability of randomizing value/bit;
+    :param n: number of users (if known in advance);
+    :param f: real frequency of value (if known in advance - not realistic in locally differentially private scenario);
+    :return: variance value.
+    """
+
     return q * (1 - q) / (n * (p - q)**2) + f * (1 - p - q) / (n * (p - q))