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Re: How to remove external parentheses from a list

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  • Subject: [mg131524] Re: How to remove external parentheses from a list
  • From: Bob Hanlon <hanlonr357 at gmail.com>
  • Date: Sat, 17 Aug 2013 02:07:43 -0400 (EDT)
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Use Sequence


limits = {{x1, a, b}, {x2, c, d}, {xn, y, z}};


Integrate[f[x1, x2, xn], Sequence @@ limits]


Integrate[f[x1, x2, xn],
   {x1, a, b}, {x2, c, d},
   {xn, y, z}]


However, Mathematica only accepts this form because Integrate does not have
the Attribute HoldAll or HoldRest.

Attributes[Integrate]


{Protected, ReadProtected}


For functions that have either of these attributes, you would also need to
use Evaluate.


Attributes[Table]


{HoldAll, Protected}


limits = {{x1, 0, 1}, {x2, 0, 1}, {xn, 0, 1}};


Table[f[x1, x2, xn], Evaluate[Sequence @@ limits]] // Flatten


{f[0, 0, 0], f[0, 0, 1], f[0, 1, 0], f[0, 1, 1], f[1, 0, 0], f[1, 0, 1],
 f[1, 1, 0], f[1, 1, 1]}



Bob Hanlon


On Fri, Aug 16, 2013 at 7:06 AM, Samuel Mark Young <sy81 at sussex.ac.uk>wrote:

>
> Hello,
>
> I'm looking for an easy way to remove the external parentheses from a
> list.  The list contains integration variables and their respective limits,
> it currently looks something like this:
>
> {{x1,a,b},{x2,c,d},...,{xn,y,z}}
>
> However, the Integrate (or NIntegrate function) in Mathematica wants me to
> write it like this:
>
> {x1,a,b},{x2,c,d},...,{xn,y,z}
> i.e. The external parentheses have been removed
>
> I've looked around online and seen suggestions for replacing the curly
> brackets "{" with a blank space " ", or using Apply (@@) but can't work out
> the correct syntax.
>
> Thanks for any help and advice!
>
> Regards,
> Sam
>
>
>




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