Hello! Please explain me why
numpy.array([1/5])[0] == 0.2is False but
numpy.array([1/5.])[0] == 0.2is True. At 2nd line of code there is point after 5.
What should I do to get true at first line of code?
Thanks a lot.
For Sage, 1/5 is a rational number, whereas 1/5. is a floating point number:
sage: (1/5).parent()
Rational Field
sage: (1/5.).parent()
Real Field with 53 bits of precisionNow, when you put them in a numpy array, they are converted to a type named numpy.float64:
sage: type(numpy.array([1/5])[0])
<type 'numpy.float64'>
sage: type(numpy.array([1/5.])[0])
<type 'numpy.float64'>As you can see, this conversion do not lead to the same approximation for 1/5 and 1/5., they seem not rounded to the same direction:
sage: numpy.float64(1/5)
0.19999999999999998
sage: numpy.float64(1/5.)
0.20000000000000001
sage: numpy.float64(0.2)
0.20000000000000001This explains your problem. There are various issues about the rounding direction in Sage and the tools its uses, and i agree there should be a general audit.
Now, if you want 1/5 to be rounded in the right direction, you can first round it using RealField() which seems more consistent than numpy.float64:
sage: numpy.array([RR(1/5)])[0] == 0.2
TrueThanks a lot!)
This has been fixed now (trac ticket #14416), so if you upgrade, you will now get:
sage: numpy.array([1/5])[0] == 0.2
True
sage: numpy.float64(1/5)
0.20000000000000001Thanks a lot!)
Asked: 11 years ago
Seen: 867 times
Last updated: Oct 19 '13
Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.