Calculation of trigonometric functions in python

Question

How does Python calculate trigonometric functions? I try to calculate using

x = ((0.1-0.001)/2)*math.sin(((1/20)*math.pi*20)+(0.5*math.pi*1))+((0.1-0.001)/2)+0.001

I'm getting

x = 0.1

why is that? in a usual calculator (radian) i'm getting 0.001

Are you running this on python 2? In python 3 I get the correct result, the problem is to with the way that the rounding is performed try adding this before your calculation `from __future__ import division` — EdChum, Mar 18 '15 at 20:23

score 4 · Accepted Answer · edited May 23 '17 at 12:21

4

In Python 2, / is integer division,you need to import __future__ .division for floating division :

>>> from __future__ import division
>>> import math
>>> x = ((0.1-0.001)/2)*math.sin(((1/20)*math.pi*20)+(0.5*math.pi*1))+((0.1-0.001)/2)+0.001
>>> x
0.001

edited May 23 '17 at 12:21

Community

1
1

answered Mar 18 '15 at 20:22

Mazdak

105,000
18
159
188

2

"You need to import `__future__ .division`". Why? – Kevin Mar 18 '15 at 20:23
Python 2 casts to integers by default when dividing integers. Python 3 does not, so we can import this floating point functionality. – Malik Brahimi Mar 18 '15 at 20:28
@MalikBrahimi yeah! this is one of most basic stuffs in python! i add the link of relative question in SO for OP! that i think its better for OP that could read all the descriptions there! still i get 2 down vote!!!!!!!!!! – Mazdak Mar 18 '15 at 20:35

score 3 · Answer 2 · edited May 23 '17 at 11:51

3

In python2.x, python takes the floor of integer division. Thus, you need to import division from the __future__ library at the top of your program.

from __future__ import division
x = ((0.1-0.001)/2)*math.sin(((1/20)*math.pi*20)+(0.5*math.pi*1))+((0.1-0.001)/2)+0.001
print x

edited May 23 '17 at 11:51

Community

1
1

answered Mar 18 '15 at 20:26

A.J. Uppal

19,117
6
45
76

2

An alternative way is to specify floats when you want a float result. So `1/20` becomes `1.0/20.0` (or `1./20.` or `1./20`). (I did upvote the answer.) You may want to change "python rounds divsion" to "python rounds *integer* division". Actually "rounds" is also not quite right. It takes the floor. – Steven Rumbalski Mar 18 '15 at 20:37
@StevenRumbalski which is what my answer says – Vidhya G Mar 18 '15 at 20:41
actually only one operand need be a float – joel goldstick Mar 18 '15 at 21:23

Vidhya G · Answer 3 · 2015-05-05T12:11:21.733

1

Just make your integers such as 2 float 2.0, else Python 2.x uses integer division, also known as floor division (rounding towards minus infinity e.g. -9/8 gives -2, 9/8 gives 1), when dividing integers by other integers (whether plain or long):

x = ((0.1-0.001)/2.0)*math.sin(((1/20.0)*math.pi*20)+(0.5*math.pi*1))+((0.1-0.001)/2.0)+0.001

and:

print x
0.001

edited May 05 '15 at 12:11

answered Mar 18 '15 at 20:30

Vidhya G

2,250
1
25
28

Calculation of trigonometric functions in python

3 Answers3