X-Git-Url: https://gerrit.fd.io/r/gitweb?p=csit.git;a=blobdiff_plain;f=resources%2Ftools%2Fpresentation%2Futils.py;h=8f5630083b0991965935fee974dc4cfe32fbd25f;hp=c350fae13543ddd09dcc744e8803b9b80b17a3c5;hb=081c29c91b7e5f78345cfdefd75625b27b5b4812;hpb=5a6c1a5a75c76e8e63f799f5c758567c1dd75b4f

diff --git a/resources/tools/presentation/utils.py b/resources/tools/presentation/utils.py
index c350fae135..8f5630083b 100644
--- a/resources/tools/presentation/utils.py
+++ b/resources/tools/presentation/utils.py
@@ -16,6 +16,7 @@
 
 import multiprocessing
 import subprocess
+import math
 import numpy as np
 import logging
 import csv
@@ -68,6 +69,32 @@ def relative_change(nr1, nr2):
     return float(((nr2 - nr1) / nr1) * 100)
 
 
+def relative_change_stdev(mean1, mean2, std1, std2):
+    """Compute relative standard deviation of change of two values.
+
+    The "1" values are the base for comparison.
+    Results are returned as percentage (and percentual points for stdev).
+    Linearized theory is used, so results are wrong for relatively large stdev.
+
+    :param mean1: Mean of the first number.
+    :param mean2: Mean of the second number.
+    :param std1: Standard deviation estimate of the first number.
+    :param std2: Standard deviation estimate of the second number.
+    :type mean1: float
+    :type mean2: float
+    :type std1: float
+    :type std2: float
+    :returns: Relative change and its stdev.
+    :rtype: float
+    """
+    mean1, mean2 = float(mean1), float(mean2)
+    quotient = mean2 / mean1
+    first = std1 / mean1
+    second = std2 / mean2
+    std = quotient * math.sqrt(first * first + second * second)
+    return (quotient - 1) * 100, std * 100
+
+
 def get_files(path, extension=None, full_path=True):
     """Generates the list of files to process.