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MathGroup Archive 2003

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RE: Perform an assigment

  • To: mathgroup at
  • Subject: [mg43893] RE: [mg43865] Perform an assigment
  • From: "David Park" <djmp at>
  • Date: Fri, 10 Oct 2003 03:06:03 -0400 (EDT)
  • Sender: owner-wri-mathgroup at


Generally, I would recommend against assigning values to your variables.
Using the Rules that the Solve routine returns is often more convenient. If
you assign values you can no longer use the variables as symbols until you
Clear them.

Nevertheless, the following is how you can do it.

eqns = {2x + 3y == 5, x - y == 2};
sols = Solve[eqns, {x, y}][[1]]
x = x /. sols
y = y /. sols

{x -> 11/5, y -> 1/5}

But now see what happens is you try to evaluate the statements again. (Say
you decided you wanted 3 x + 3 y in the first equation.)
Instead, you can use the rules to substitute into expressions on a
controlled basis and continue to use x and y as symbolic variables.

Clear[x, y]
sols = Solve[eqns, {x, y}][[1]]

x^2 + 3x y /. sols

David Park
djmp at

From: paulocct at [mailto:paulocct at]
To: mathgroup at

Hi all,
I want to solve a system of equations and to assign the values
calculated to the variables of the system automatically, What should I
do?. What command should I use?

Thanks a lot,

Paulo Carmona
University of Quindio

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