R help - Mar 2008 - generate random numbers subject to constraints

I am trying to generate a set of random numbers that fulfill the following
constraints:

X1 + X2 + X3 + X4 = 1

aX1 + bX2 + cX3 + dX4 = n

where a, b, c, d, and n are known.

Any function to do this?

Thanks,
-Ala'

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I am trying to generate a set of random numbers that fulfill the
following constraints:

X1 + X2 + X3 + X4 = 1

aX1 + bX2 + cX3 + dX4 = n

where a, b, c, d, and n are known.

Any function to do this?

Thanks,
-Ala'

At 01:13 PM 3/26/2008, Ala' Jaouni wrote:
>I am trying to generate a set of random numbers that fulfill the following
>constraints:
>
>X1 + X2 + X3 + X4 = 1
>
>aX1 + bX2 + cX3 + dX4 = n
>
>where a, b, c, d, and n are known.
>
>Any function to do this?
1. Generate random variates for X1, X2, based upon whatever 
unspecified distribution you wish.

2. Solve the two equations for X3 and X4.

===============================================================Robert A.
LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral at lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"

X1,X2,X3,X4 should have independent distributions. They should be
between 0 and 1 and all add up to 1. Is this still possible with
Robert's method?

Thanks