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MathGroup Archive 2002

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Re: elementwise vector scalar subtraction

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35640] Re: elementwise vector scalar subtraction
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Wed, 24 Jul 2002 02:06:00 -0400 (EDT)
  • References: <ahj04h$goi$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Oscar,
Some suggestions:

    t = {0, 1, 1.5, 2, 2.5, 4};
    c = {a, b};

    TC[t_, c_] :=
       Module[{u},
           u = Transpose[ReleaseHold[t + Hold[c]]];
           u[[All,1]] = t[[1]]; u
        ]

Test:
    TC[t, c]

        {{0, 1 + a, 1.5 + a, 2 + a, 2.5 + a, 4 + a},
          {0, 1 + b, 1.5 + b, 2 + b, 2.5 + b, 4 + b}}

To  include assigning values to tca, tcb we may use

    TC1[t_, c_] :=
        Module[{u},
            Clear["`tc*"];
            u = Transpose[ReleaseHold[t + Hold[c]]];
            u[[All,1]] = t[[1]];
            Evaluate[ToExpression[(StringJoin["tc", ToString[#1]] & ) /@ c]]
= u
        ];
        (*the use of Evaluate is because in evaluating an expression
h[e,...]=rhs or h[e,...]:= expr the evaluation of
h[e,...] stops after evaluating the heads and the elements (at
h*[e*,...]) --- otherwise we could not re-define. It could have been avoided
by introducing another symbol, v say, with v = ToExpression[ ...]; v=u*)

Test:
    TC1[t, c]

        {{0, 1 + a, 1.5 + a, 2 + a, 2.5 + a, 4 + a},
          {0, 1 + b, 1.5 + b, 2 + b, 2.5 + b, 4 + b}}

    tca

        {0, 1 + a, 1.5 + a, 2 + a, 2.5 + a, 4 + a}

It may be more convenient to use indexed symbols:

    TC2[t_, c_] :=
        Module[{u},
            u = Transpose[ReleaseHold[t + Hold[c]]];
            u[[All,1]] = t[[1]];
            Evaluate[tc /@ c] = u
     ];

    TC2[t, c]

        {{0, 1 + a, 1.5 + a, 2 + a, 2.5 + a, 4 + a},
          {0, 1 + b, 1.5 + b, 2 + b, 2.5 + b, 4 + b}}

    tc[a]

        {0, 1 + a, 1.5 + a, 2 + a, 2.5 + a, 4 + a}

--
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


"O.A. Linares, M.D., Ph.D." <divinesaam at aol.com> wrote in message
news:ahj04h$goi$1 at smc.vnet.net...
> Dear Colleagues,
>
> I have a t-vector
>
> t = {0, 1, 1.5, 2, 2.5, 4, 6, 8, 10, 15, 20, 30};
>
> I want to subtract 0.15 from each element except the first to get
>
> tc15 = {0, 1 - 0.15, 1.50 - 0.15, 2 - 0.15, 2.5 - 0.15, 4 - 0.15, 6 -
> 0.15, 8 - 0.15, 10 - 0.15, 15 - 0.15, 20 - 0.15, 30 - 0.15};
>
> I then want to subtract 0.20 to get
>
> tc20 = {0, 1 - 0.20, 1.50 - 0.20, 2 - 0.20, 2.5 - 0.20, 4 - 0.20, 6 -
> 0.20, 8 - 0.20, 10 - 0.20, 15 - 0.20, 20 - 0.20, 30 - 0.20};
>
> Is there a way to automate this process for n subtractions from 0.15
> to 0.30 to yield individual t-vectors for tc15 through tc30 ?
>
> With Much Appreciation,
>
> Oscar
>




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