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Re: Subscript Bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90123] Re: Subscript Bug?
  • From: David Bailey <dave at Remove_Thisdbailey.co.uk>
  • Date: Mon, 30 Jun 2008 04:51:14 -0400 (EDT)
  • References: <g47l28$t66$1@smc.vnet.net>

Aaron Fude wrote:
> Hi,
> 
> I have this code in a cell:
> 
> Subscript[H, 1] = 110; Subscript[H, 2] = 90;
> H = Subscript[H, 1] + Subscript[H, 2];
> Tanh[Subscript[H, 1]]
> 
> The first time I execute the cell, I get
> 
> Tanh[Subscript[200, 1]]
> 
> which of course is nonsense.
> 
> A second execution, yields the correct answer:
> 
> Tanh[110]
> 
> Is this a feature that I don't understand or a bug?
> 
Well I guess you should class it as a feature you don't understand!

The first time though you make the following assignments:

Subscript[H, 1] = 110
Subscript[H, 2] = 90
H0

The second time through, H has a value, so make the assignment:

Subscript[200, 1] = 110
Subscript[200, 2] = 90
H0

Therefore on the second execution Subscript[200, 1] evaluates to 110.

The moral of this story is that if you want to define Subscript[var,n], 
it doesn't make mush sense to proceed to give a value to var itself!

David Bailey
http://www.dbaileyconsultancy.co.uk




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