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MathGroup Archive 2001

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Re: Searching for embedded zeros in list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32156] Re: Searching for embedded zeros in list
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Sun, 30 Dec 2001 02:54:20 -0500 (EST)
  • References: <a0jlsc$31m$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Mark,

a = {0.98, 0.87, 0.0, 0.5, 0.25};
b = {0.9, 0.0, 0.0, 0.0, 0.0, 0.0, 0.05};
c = {0.75, 0.42, 0.10, 0.0, 0.03};
d = {0.0, 0.90, 0.75, 0.42, 0.25, 0.0};

Cases[{a,b,c,d}, {___,x_/;x=!=0.,___,0.,___,y_/;y=!=0.,___}]


{{0.98,0.87,0.,0.5,0.25},{0.9,0.,0.,0.,0.,0.,0.05},{0.75,0.42,0.1,0.,0.03}}

Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565


"Coleman, Mark" <mark.coleman at dri-wefa.com> wrote in message
news:a0jlsc$31m$1 at smc.vnet.net...
> Greetings,
>
> Can anyone suggest an efficient/elegant way of checking a list for
> 'embedded' zeros. By embedded I mean the occurence of one or more zeros
> between two non-zero elements (note: zeros at the ends of the list are
> not relevant). For instance, the following lists all contain embedded
> zeros:
>
>    a={0.98,0.87,0.0,0.5,0.25}
>    b={0.9,0.0,0.0,0.0,0.0,0.0,0.05}
>    c={0.75,0.42,0.10,0.0,0.03}
>
> while this list does not d={0.0,0.90,0.75,0.42,0.25,0.0}
>
> By way of background, I am working on a problem involving estimating
> generators for Markov transition matrices. One condition that ensures
> that a generator *does not* exist is the presence of inaccessible states
> in any row of the matrix. Thus one need only find a single occurance of
> an inaccessible state to show that a generator does not exist. Hence the
> code need only locate one such state, not all of them.
>
> The Mathematica code I've written for this problem does work, but it is
hardly
> "elegant".
>
> Any help would be much appreciated!
>
> Best regards,
>
> -Mark
>
>






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