       Re: Bug in Sum?

• To: mathgroup at smc.vnet.net
• Subject: [mg109146] Re: Bug in Sum?
• From: "Tony Harker" <a.harker at ucl.ac.uk>
• Date: Mon, 19 Apr 2010 04:11:26 -0400 (EDT)

What version are you using? 7.0 for Microsoft Windows (32-bit) (February 18,
2009) gives identical, correct, results for both.

Tony Harker

]-> -----Original Message-----
]-> From: gopher [mailto:gophergoon at gmail.com]
]-> Sent: 13 April 2010 04:04
]-> To: mathgroup at smc.vnet.net
]-> Subject: [mg109109] Bug in Sum?
]->
]-> In the following, A and Expand[A] give different answers after when
]-> summed (a finite geometric series.) The result of summing A
]-> is clearly
]-> wrong, since it is independent of the parameters r and s.
]->
]-> Abhishek
]->
]-> In:= A = x^(i - n) (x^(i - n) (1 - r x^n) - s);
]-> A == Expand[A] // Simplify
]->
]-> Out= True
]->
]-> In:= Sum[A, {i, 0, n - 1}]
]->
]-> Out= (x^(-2 n) (-1 + x^(2 n)))/(-1 + x^2)
]->
]-> In:= Sum[Expand[A], {i, 0, n - 1}] // FullSimplify
]->
]-> Out= -((
]->  x^(-2 n) (-1 + x^n) (-1 + x^n (-1 + r + s + s x + r
]-> x^n)))/(-1 + x^2)
]->  )
]->
]->

• Prev by Date: Exporting Plot with Customized Legend to PDF
• Next by Date: Re: Bug in Sum?
• Previous by thread: Bug in Sum?
• Next by thread: Re: Bug in Sum?