# [SciPy-user] Solve

lorenzo bolla lbolla@gmail....
Tue Nov 6 09:45:39 CST 2007

```Maybe I'm misunderstanding, but it seems you look at solve(a,b) as a
function to return the solution of the linear symbolic equation: a * x = b
(whose solution is: x = b / a), with x scalar.
Instead, solve(a,b) gives the numerical solution of the linear system a * x
= b, with x and b 1d-arrays and a 2d-array. For examples, something like:
2 * x1 + 3 * x2 = 4
4 * x1 + 5 * x2 = 6
where x = [x1, x2], b = [4, 6] and a = [[2, 3], [4, 5]]. solve(a,b) returns
[-1, 2].

If from the file you import a string with the symbolic representation of you
equation, and you want to solve it symbolically, stay with simpy.
hth,
L.

On 11/6/07, Eduardo Rodrigues <elr1979@gmail.com> wrote:
>
>  If I want to solve an equation with linalg.solve I must know the
> equation, right?
>
> From help:
> "solve(a, b)
>     Return the solution of a*x = b"
>
>  But if I don't know - or if I don't want to look - the equation for x,
> how can I solve it?
> I will import equations from a file.
>
> []'s.
>
>
>
>
>
> ----- Original Message -----
> *From:* Michael Nandris <mnandris@btinternet.com>
> *To:* SciPy Users List <scipy-user@scipy.org>
> *Sent:* Tuesday, November 06, 2007 10:42 AM
> *Subject:* Re: [SciPy-user] Solve
>
>
> These examples for solving equations are in *scipy_tutorial.pdf*
>
> from scipy import mat, linalg
>
> """
> Solves three simultaneous equations:
>     x + 3y + 5z = 10
>     2x + 5y + z = 8
>     2x + 3y + 8z =3
> """
>
> XYparameters = mat('[1 3 5; 2 5 1; 2 3 8]')
> constants = mat('[10; 8; 3]')
> print linalg.solve( XYparameters, constants )
>                                         # array([[-9.28],
>                                         #        [ 5.16],
>                                         #      [ 0.76]])
>
> """
> Solves two simultaneous equations:
>     5x + 2y - 9 = 0
>     3x + 4y - 4 = 0
> """
>
> XYparameters = mat('[5 2; 3 4]')
> constants = mat('[9; 4]')
> print linalg.solve( XYparameters, constants )  # should print (2,-0.5)
>
> *Eduardo Rodrigues <elr1979@gmail.com>* wrote:
>
> Hi, I am starting in Python. I usually use Maple and I am with a problem
> to
> do the same project in Python.
> I would like to solve an equation like x+y+1=0 for x. In Maple I use
> "solve(x+y+1=0,x);".
> Do exist a similar command in Python/NumPy/SciPy?
> Regards,
> Eduardo.
>
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