#12724: Allow different normalizations for Eisenstein series q-expansion
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   Reporter:  davidloeffler  |             Owner:  craigcitro    
       Type:  enhancement    |            Status:  new           
   Priority:  major          |         Milestone:  sage-5.0      
  Component:  modular forms  |          Keywords:                
Work issues:                 |   Report Upstream:  N/A           
  Reviewers:                 |           Authors:  David Loeffler
  Merged in:                 |      Dependencies:                
   Stopgaps:                 |  
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 This came up as part of my review of #12046, but it's of independent
 interest.

 The level 1 Eisenstein series can be normalized in three natural ways: so
 the linear term is 1; so the constant term is 1; or so the coefficients
 are integers with no common factor. Renormalizing is no problem if you're
 working over QQ but over finite characteristic base rings it is a total
 pain (try computing E_p-1_ mod p^2^).

 The patch below modifies {{{ eisenstein_series_qexp }}} so the following
 works:
 {{{
 sage: eisenstein_series_qexp(6, 5, normalization="constant")
 1 - 504*q - 16632*q^2 - 122976*q^3 - 532728*q^4 + O(q^5)
 sage: eisenstein_series_qexp(6, 10, K=Zmod(49), normalization="constant")
 1 + 35*q + 28*q^2 + 14*q^3 + 42*q^5 + 21*q^6 + 35*q^7 + 35*q^8 + 7*q^9 +
 O(q^10)
 }}}

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12724>
Sage <http://www.sagemath.org>
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