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Beginner--Error in Series expansion

  • To: mathgroup at smc.vnet.net
  • Subject: [mg68155] Beginner--Error in Series expansion
  • From: abdou.oumaima at hotmail.com
  • Date: Wed, 26 Jul 2006 02:26:19 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello mathgroup,

When I'm trying to find a power series of this function, It doesn't yield the correct expression:

Z[L_] = Sum[(((-1)^Lp/(
      L - Lp + 1))*(1/ksi^Lp)), {Lp, 0, L}] - (-1)^L Log[1 + ksi]/ksi^(L + 1)

devZ[L_] = Normal[Series[Z[L], {ksi, 0, 2}]]
devZ[3]

I get: devZ[3]= 1/4 -1/ksi^3+1/2 ksi +(ksi-ksi^2/2)/ksi^4.
This code must yield:
devZ[3]= ksi/5 - ksi^2/6 +0(ksi^3)

How to correct this error.

Any help will be very welcome.

Lian.




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