the output of this
d=3
for n in range (1,d):
print n,d,n/d
is correctly
1 3 1/3
2 3 2/3
on the other hand, the output of this
for d in range(2,4):
for n in range(1,d):
print n,d,n/d
is
1 2 0
1 3 0
2 3 0
why, in this case, is the ratio n/d always zero?
('Sage Version 5.10, Release Date: 2013-06-17', firefox 23.0, osx 10.6.8)
I would say that it is because
type(d)
does not return the same thing in the two cases. There are different forms of integers in Sage, and it can be tricky from time to time : there are for instance "python" integers (i.e. int(6)) and Sage integers (i.e. Integer(6)).
The range function, in particular, only returns Python integers
sage: int(9)/int(4)
2
While you probably want to use Sage integers instead, which knows when they should consider themselves as rational numbers
sage: Integer(9)/Integer(4)
9/4
Sooooooo if you want to change your code a bit, I would say that you can fix it by replacing {{{range(something)}}} by {{{srange(something)}}}. srange returns Sage integers :-)
sage: map(type,range(4))
[int, int, int, int]
sage: map(type,srange(4))
[sage.rings.integer.Integer,
sage.rings.integer.Integer,
sage.rings.integer.Integer,
sage.rings.integer.Integer]
Nathann
Using print n,d,type(n/d), I am seeing that in the first case, Sage treats the values in sage.rings.rational.Rational and so you get the output you want. In the second case, Sage treats the values as integers and so the division gives the integer quotient.
What I don't know is why Sage is making these particular interpretations in these cases. Perhaps others can give us an idea of why this is happening.
Asked: 2013-08-14 08:01:23 +0100
Seen: 935 times
Last updated: Aug 14 '13
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