#16671: implement harmonic number function H(n,m)
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Reporter: rws | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.3
Component: symbolics | Resolution:
Keywords: special, log | Merged in:
Authors: Ralf Stephan | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/rws/implement_harmonic_number_function_h_n_m_|
0c93bfe4da1bd2b3a77865ae0a6878007726fff8
Dependencies: | Stopgaps:
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Comment (by nbruin):
Replying to [comment:13 rws]:
> Replying to [comment:9 nbruin]:
> > Can't you get that conversion by giving an appropriate
`sage.symbolic.pynac.register_symbol`?
> Is there ready mechanics for this? I can't find one. Do you expect me to
implement it?
No, just use it. If you do `search_src("register_symbol")` you get a few
hits on its use. The following seems to basically work without your patch
so I hope you can adjust it for your purposes:
{{{
sage: var('x,t,s')
(x, t, s)
sage: function('g')
g
sage: def swap(a,b): return g(b,a)
sage:
sage.symbolic.pynac.register_symbol(swap,{'maxima':'gen_harmonic_number'})
sage: sum(1/t^2,t,1,s)
g(s, 2)
}}}
That way, the parsing won't be more broken than for other functions (and
it seems we're doing fine for most expressions nowadays). The regex for
`psi` isn't really wrong, because it specifies there should be only digits
between the square brackets. It is perhaps a little overly restrictive,
though:
{{{
sage: psi(x,s)
psi(x, s)
sage: maxima_calculus(psi(x,s))
psi[x](s)
sage: maxima_calculus(psi(x,s))._sage_()
TypeError: unable to make sense of Maxima expression 'psi[x](s)' in Sage
sage: from sage.interfaces.maxima_lib import max_to_sr
sage: max_to_sr(maxima_calculus(psi(x,s)).ecl()) #this doesn't rely on
parsing or regexes
psi(x, s)
}}}
I think "parsing" psi via regex was just a quick fix around the fact that
the expression parser doesn't know what to do with square brackets (and
since they're rare, you can get away with not really parsing them
properly). In your case, round brackets are so common that you'll quickly
get caught if you don't deal with them properly. Luckily, the parser knows
how to deal with them, you just have to swap the arguments.
--
Ticket URL: <http://trac.sagemath.org/ticket/16671#comment:14>
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