[Maxima-discuss] incorrect taylor(expintegral_si...)

[Robert L. <Rob...@t-...>]

Hello,

  is the following mismatch a bug ?
  where might this be ?
  I've not seen something like a deftaylor for expintegral_si
    in the maxima source code, and the diff(expintegral_si) seems to be ok.
  So I'm wondering why taylor fails.

  note, numerical evaluation of expintegral_si does match with
    the abramowitz series expansion.
 
Regards,
  Robert Larice
  
/* (browse-url-xdg-open "/home/linux/Downloads/AMS55.djvu")
 * Abramowitz 5.2.14
 */

Si_abramowitz(z) := sum((-1)^k * z^(2*k+1) / ((2*k+1)*(2*k+1)!), k, 0, inf);

/* these don't match */
T_Si_maxima : taylor(expintegral_si(z), z, 0, 9);
T_Si_abramowitz : taylor(Si_abramowitz(z), z, 0, 9);