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Re: Subscript Bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90124] Re: [mg90111] Subscript Bug?
  • From: Carl Woll <carlw at wolfram.com>
  • Date: Mon, 30 Jun 2008 04:51:25 -0400 (EDT)
  • References: <200806290936.FAA29888@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.
>  
>
The first time you execute the cell, the assignment

H = Subscript[H, 1] + Subscript[H, 2];

sets H to 110 + 90, which is 200. Then, Tanh[Subscript[200,1]] is what 
you get.

The second time you execute the cell, H is 200, so Subscript[200,1] is 
set to 110 and Subscript[200,2] is set to 90. Then, H is set to 200 
again. Now, Subscript[H,1] is Subscript[200,1] which equals 110, so you 
get Tanh[110].

If you want to do these kinds of manipulations with Subscript, then I 
recommend that you give Subscript the HoldFirst attribute.

Carl Woll
Wolfram Research

>A second execution, yields the correct answer:
>
>Tanh[110]
>
>Is this a feature that I don't understand or a bug?
>  
>



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