#15970: j_invariant_qexp won't allow substitution
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Reporter: katestange | Owner:
Type: defect | Status: needs_review
Priority: minor | Milestone: sage-6.2
Component: number theory | Resolution:
Keywords: j-invariant, | Merged in:
laurent series, q-expansion, | Reviewers:
substitution | Work issues:
Authors: Alex Ghitza | Commit:
Report Upstream: N/A | 831373cb2b46477eb713b557765aa1439d1f627f
Branch: | Stopgaps:
u/AlexGhitza/ticket/15970 |
Dependencies: |
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Comment (by nbruin):
Replying to [comment:2 katestange]:
> How can one approximate the j-invariant for various tau in the upper
half plane? This is something Sage ought to allow someone to do, in some
fashion, so if isn't possible, then maybe this ticket should be changed to
a requested feature.
The request is of course a reasonable one. Sometimes all you have is a
finite approximation, and evaluating that will be the best you'll get. The
trick is to get rid of the `O(..)` term, which you can do with `truncate`:
{{{
sage: jq = j_invariant_qexp(10)
sage: jq.truncate(100)(e^(-2*pi)).n()
1727.99999999999
}}}
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Ticket URL: <http://trac.sagemath.org/ticket/15970#comment:7>
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