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MathGroup Archive 1999

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Re: problem with Part function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18186] Re: problem with Part function
  • From: "Michael J Hirsch" <M_HIRSCH at prodigy.net>
  • Date: Mon, 21 Jun 1999 22:50:31 -0400
  • Organization: Prodigy Internet http://www.prodigy.com
  • References: <7kho9q$qop@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Casubolo Dario wrote in message <7kho9q$qop at smc.vnet.net>...
>
>Just a little problem:
>I've a matrix of zeros, say:
>mat=Table[Table[0,{5}],{5}];
>then, I've a point in xy axys,
>xy={3,3};
>now, I want the position {3,3} of matrix becomes 1;
>if I write
>mat[[xy]]=1; or mat[[{3,3}]]=1; it doesn't work; only mat[[3,3]]=1
>works, but I don't want rewrite all.
>I think I've to use something like Map, Thread, Apply or so, but I don't
>know what and how exactely;
>please, someone help me.
>THANK YOU
>
>Dario Casubolo
>email: bubbola at workline.it
>
>

>

Dario:

Accessing a specific part of a matrix can be done in a number of very
similar ways:

    If you only are accessing one entry, you can do it in the following way:

            mat[[row_#,col_#]] = alpha, where alpha is whatever you want to
put in the matrix.

    If you have more than one row, but only one column, you can do it in the
following way:

            mat[[{row_list},col_#]] = alpha, where alpha is an appropriately
sized matrix.

    And there are similar ways if you have more than one column.

    For your specific example, you want

        mat[[ xy[[1]] , xy[[2]] ]] = 1

    I hope this helps!

            Michael J. Hirsch
            AMPAC, Inc.
            m_hirsch at prodigy.net





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