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Re: Table local

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113809] Re: Table local
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sun, 14 Nov 2010 06:07:43 -0500 (EST)

http://reference.wolfram.com/mathematica/ref/Table.html

"Table[expr, spec] first evaluates spec, then localizes the variable specified, and successively assigns values to it, each time evaluating expr."

In other words, what is localized is the index i

Clear[i, u];
Table[u = i^2, {i, 5}];
{i, u}

{i, 25}

Clear[i, u];
u = 0; Table[u += i^2, {i, 5}];
{i, u}
u == Sum[i^2, {i, 5}]

{i, 55}

True


Bob Hanlon

---- EF <he.frauendorfer at t-online.de> wrote: 

=============
"Help, More Information" for Table states:

  Table effectively uses Block to localize values or variables.

   But
   Clear[u];
   Table[u = i^2, {i, 5}];
   u

   Clear[u];
   Table[u = i^2;, {i, 5}];
   u

   In both cases the value 25 for u is given.
   If u were really local, it should have no value outside of the Table


   For me there is a contradiction that can cause a lot of trouble


   E. F.




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