Why math.ceil() give different answers

Question

I am new to python. I was trying to solve a matrix problem in which I have to use exit condition in loop for example if column and row of matrix is 3 or 4 then i want to run the loop 2 times and if col and row is 5 or 6 then it run 3 times.

>>> math.ceil(1.5)
2.0
>>> i=3
>>> math.ceil(i/2)
1.0

score 3 · Accepted Answer · edited May 23 '17 at 12:29

3

This is because 3 / 2 isn't 1.5 in Python 2, it's 1. Do from __future__ import division and then it'll be what you expect.

edited May 23 '17 at 12:29

Community

1
1

answered Dec 06 '13 at 07:18

Danica

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why it so ?What is reason behind this? – InvisibleWolf Dec 06 '13 at 07:33
3

@vj1207 [Here is an explanation](http://python-history.blogspot.com/2009/03/problem-with-integer-division.html) by Guido. – user4815162342 Dec 06 '13 at 07:49

user2684206 · Answer 2 · 2013-12-06T07:25:18.867

0

try this first:

i=3/2
print i
j=float(3)/2
print j
print math.ceil(j)

you should see

1
1.5
2.0

the way python deals with integer division is taking the lower bound.

Reference:

http://docs.python.org/2/reference/expressions.html

edited Dec 06 '13 at 07:25

answered Dec 06 '13 at 07:19

user2684206

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Correct. Note the **lower** part. Integer division in Python rounds towards -infinite for negative values, **not** towards 0. – Steinar Lima Dec 06 '13 at 10:13

Why math.ceil() give different answers

2 Answers2