On 8/6/13 8:10 AM, John Cremona wrote:
I really hope there is some clearer documentation than those code
comments, since I am even more confused after reading that than after
seeing the original post.
sage: a = RIF(1.332,1.334)
sage: a.center()
1.33300000000000
sage: a
1.34?
The center is 1.33 and we know that the value is "really" between
1.332 and 1.334 so the first two decimal places after the point are
certainly 33. How on earth is 1.34? supposed to convey that?
First of all, note that 1.333? would not be valid since the right
endpoint is really 1.3340000000000001 (1.334 is not exactly
representable, and it is rounded up). So we're deciding between 1.33?
and 1.34?. The way I understand it, since they both have the same
precision, the number farther from zero is picked. I think I agree with
you, though, that in this case having a number that is more central is
more important than picking the number farthest from zero.
It would make more sense to ask if the lower endpoint of the printed
representation is the same sign as the upper endpoint of the printed
representation (e.g., sign(1.33-.01)==sign(1.33+.01)), and if it is, use
the more natural 'center' point (i.e., the number closer to the center
of the interval), instead the point farthest from zero. Then we get
intervals that are obviously all the same sign when it's important, and
more natural representations otherwise.
On Sage 5.11.beta3 I get
sage: a = RIF(0,123)
sage: a
1.?e2
and not '62.?62' which I suppose is intended to convey "61.5
plus-or-minus 61.5'. So is that comment in the code out of date?
Note that it says "with 2 error digits":
sage: RIF(0,123).str(error_digits=2)
'62.?62'
I think the interval arithmetic is great, and very useful, but the
output format is so bizarre I wonder whether if it is putting users
off using it.
That's a good question; anyone else want to comment? You can also
change the default formatting by setting a module variable.
sage: sage.rings.real_mpfi.printing_style='brackets'
sage: RIF(0,123)
[0.00000000000000000 .. 123.00000000000000]
Thanks,
Jason
--
You received this message because you are subscribed to the Google Groups
"sage-devel" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sage-devel+unsubscr...@googlegroups.com.
To post to this group, send email to sage-devel@googlegroups.com.
Visit this group at http://groups.google.com/group/sage-devel.
For more options, visit https://groups.google.com/groups/opt_out.
