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From: Bob Hanlon on 3 May 2010 06:11

Array[((-1)^(# + 1) (x)^#)/#! &, 3, 1] // Total

x^3/6 - x^2/2 + x

Plus @@ Array[((-1)^(# + 1) (x)^#)/#! &, 3, 1]

x^3/6 - x^2/2 + x

Sum[(-1)^(n + 1) x^n/n!, {n, 3}]

x^3/6 - x^2/2 + x

Series[1 - E^-x, {x, 0, 3}] // Normal

x^3/6 - x^2/2 + x

% == %% == %%% == %%%%

True


Bob Hanlon

---- davef <davidfrick2003(a)yahoo.com> wrote:

=============
I want to evaluate a sum from a series I created using the Array
function.

For example; I specify

Array[((-1)^(# + 1) (x)^#)/# ! &, 3, 1 ]

which gives me the following 3 terms of output:

{x, -(x^2/2), x^3/6}

Can anyone tell if and how I can turn these 3 terms into a sum to be
evaluated?



From: Laszlo Sturmann on 3 May 2010 06:12
davef wrote:
> I want to evaluate a sum from a series I created using the Array
> function.
>
> For example; I specify
>
> Array[((-1)^(# + 1) (x)^#)/# ! &, 3, 1 ]
>
> which gives me the following 3 terms of output:
>
> {x, -(x^2/2), x^3/6}
>
> Can anyone tell if and how I can turn these 3 terms into a sum to be
> evaluated?
>
>
>
Apply[Plus, Array[((-1)^(# + 1) (x)^#)/#! &, 3, 1]]

LS

From: Murray Eisenberg on 3 May 2010 06:11
Very simple:

Apply[Plus, Array[((-1)^(# + 1) (x)^#)/# !&, 3, 1 ]]

Or, using the prefix @@ abbreviation for Apply:

Plus @@ Array[((-1)^(# + 1) (x)^#)/#! &, 3, 1]

Or, with a newer specialized function in Mathematica:

Total[Array[((-1)^(# + 1) (x)^#)/#! &, 3, 1]]

Or:

Total @ Array[((-1)^(# + 1) (x)^#)/#! &, 3, 1]

On 5/2/2010 5:35 AM, davef wrote:
> I want to evaluate a sum from a series I created using the Array
> function.
>
> For example; I specify
>
> Array[((-1)^(# + 1) (x)^#)/# !&, 3, 1 ]
>
> which gives me the following 3 terms of output:
>
> {x, -(x^2/2), x^3/6}
>
> Can anyone tell if and how I can turn these 3 terms into a sum to be
> evaluated?
>

--
Murray Eisenberg murray(a)math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower phone 413 549-1020 (H)
University of Massachusetts 413 545-2859 (W)
710 North Pleasant Street fax 413 545-1801
Amherst, MA 01003-9305

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