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Re: RecurrenceTable warning

  • To: mathgroup at smc.vnet.net
  • Subject: [mg102494] Re: [mg102430] RecurrenceTable warning
  • From: dkapadia at wolfram.com
  • Date: Tue, 11 Aug 2009 04:04:51 -0400 (EDT)
  • References: <200908091005.GAA15916@smc.vnet.net>

> Hello, I'm using Mathematica 7.0.1.
>
> This example is in documentation center.
>
> In[1]:= RecurrenceTable[{a[n + 1] == 3 a[n], a[1] == 7}, a, {n, 1, 5}]
> Out[1]= {7, 21, 63, 189, 567}
>
>
> I added a[n]==b[n].
>
> In[2]:= RecurrenceTable[{b[n] == a[n], a[n + 1] == 3 a[n],
>   a[1] == 7}, {a, b}, {n, 1, 5}]
> Out[2]= {{7, 7}, {21, 21}, {63, 63}, {189, 189}, {567, 567}}
>
>
> it works well.
> but when I simply swapped a with b, a warning occured.
>
> In[3]:= RecurrenceTable[{a[n] == b[n], b[n + 1] == 3 b[n],
>   b[1] == 7}, {b, a}, {n, 1, 5}]
>
> During evaluation of In[3]:= Inverse::matsq: Argument {{1/4,1,-1},
> {1/4,0,1}} at position 1 is not a non-empty square matrix. >>
>
> Out[3]= {{7, 7}, {21, 21}, {63, 63}, {189, 189}, {567, 567}}
>
>
Hello,

Thank you for reporting the above problem with RecurrenceTable.

The unexpected Inverse::matsq message is generated while trying to solve
the equations with a and b swapped, as a system of difference-algebraic
equations.

I apologize for the confusion caused by this problem, which clearly needs
to be fixed.

Sincerely,

Devendra Kapadia,
Wolfram Research, Inc.



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