Log to the base 2 in python

Question

How should I compute log to the base two in python  Eg  I have this equation where I am using log base 2  import math e   - t T   math log  t T    2

User · Answer

In python 3 or above  math class has the following functions import math  math log2 x  math log10 x  math log1p x   or you can generally use math log x  base  for any base you want

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http   en wikipedia org wiki Binary logarithm  def lg x  tol 1e-13     res   0 0      Integer part   while x lt 1      res -  1     x    2   while x gt  2      res    1     x    2      Fractional part   fp   1 0   while fp gt  tol      fp    2     x    x     if x  gt   2          x    2         res    fp    return res

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If you are on python 3 3 or above then it already has a built-in function for computing log2 x  import math  finds log base2 of x  answer   math log2 x   If you are on older version of python then you can do like this import math  finds log base2 of x  answer   math log x  math log 2

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It s good to know that    but also know that math log takes an optional second argument which allows you to specify the base   In  22   import math  In  23   math log  Type        builtin function or method Base Class   lt type  builtin function or method  gt  String Form      lt built-in function log gt  Namespace   Interactive Docstring      log x   base   - gt  the logarithm of x to the given base      If the base not specified  returns the natural logarithm  base e  of x    In  25   math log 8 2  Out 25   3 0

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float   float math log2 x  import math  log2   math log x  2 0  log2   math log2 x      python 3 3 or later   Thanks  akashchandrakar and  unutbu    float   int math frexp x  If all you need is the integer part of log base 2 of a floating point number  extracting the exponent is pretty efficient  log2int slow   int math floor math log x  2 0    log2int fast   math frexp x  1  - 1   Python frexp   calls the C function frexp   which just grabs and tweaks the exponent   Python frexp   returns a tuple  mantissa  exponent   So  1  gets the exponent part   For integral powers of 2 the exponent is one more than you might expect   For example 32 is stored as 0 5x26   This explains the - 1 above   Also works for 1 32 which is stored as 0 5x2 4    Floors toward negative infinity  so log231 computed this way is 4 not 5   log2 1 17  is -5 not -4     int   int x bit length   If both input and output are integers  this native integer method could be very efficient  log2int faster   x bit length   - 1   - 1 because 2n requires n 1 bits  Works for very large integers  e g  2  10000   Floors toward negative infinity  so log231 computed this way is 4 not 5

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Using numpy   In  1   import numpy as np  In  2   np log2  Type            function Base Class       lt type  function  gt  String Form      lt function log2 at 0x03049030 gt  Namespace       Interactive File            c  python26 lib site-packages numpy lib ufunclike py Definition      np log2 x  y None  Docstring      Return the base 2 logarithm of the input array  element-wise   Parameters ---------- x   array like   Input array  y   array like   Optional output array with the same shape as  x    Returns ------- y   ndarray   The logarithm to the base 2 of  x  element-wise    NaNs are returned where  x  is negative   See Also -------- log  log1p  log10  Examples --------  gt  gt  gt  np log2  -1  2  4   array   NaN    1     2     In  3   np log2 8  Out 3   3 0

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Don t forget that log base A  x   log base B  x   log base B  A   So if you only have log  for natural log  and log10  for base-10 log   you can use  myLog2Answer   log10 myInput    log10 2

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Try this    import math print math log 8 2      math log number base

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gt  gt  gt  def log2  x            return math log  x     math log  2         gt  gt  gt  log2  2   1 0  gt  gt  gt  log2  4   2 0  gt  gt  gt  log2  8   3 0  gt  gt  gt  log2  2 4   1 2630344058337937  gt  gt  gt

[python] Log to the base 2 in python

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