Re: algebraic manipulator in octave

[Geraint Paul Bevan]

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Paul Kienzle wrote:
|
| On Feb 21, 2004, at 3:15 PM, Arnau Mir wrote:
|
|> Hello.
|>
|> Can I use octave as algebraic manipulator?
|> For example, can I make with octave the following:
|>
|> a x^2+b x+c=0
|>
|> and octave responses a solution as a function of a,b c?
|
|
| octave-forge (http://octave.sf.net) has a symbolic
| package which is a wrapper around GiNaC.  It
| preserves symbols through mathematical operations.
| Later you can substitute values for the symbols.
|
| It looks to have some numeric solvers, but I don't
| see anything to solve for x symbolically.
|
| Paul Kienzle
| address@hidden
|


I have just tried using ginsh directly to solve this equation, but it
seems that ginsh can only solve linear systems:

| lsolve ( { a*x^2 + b*x + c == 0 } , { x } );
lsolve: system is not linear



This seems to agree with the GiNaC tutorial pages
(http://www.ginac.de/tutorial) which state that lsolve is just a wrapper
for matrix::solve which "linear systems may be solved with".

Therefore, I doubt that any of the Octave interfaces to GiNaC/ginsh will
be able to solve this problem symbolically.


Maxima (http://maxima.sourceforge.net) is capable of solving the
problem, but I do not know of any Octave interface to it,

(C1) solve ( a*x^2 + b*x + c , x );

                         2                         2
                   SQRT(b  - 4 a C) + b      SQRT(b  - 4 a C) - b
(D1)        [x = - --------------------, x = --------------------]
                           2 a                       2 a


Another package, Reduce (http://www.uni-koeln.de/REDUCE/) is also
certainly capable of solving non-linear expressions, but is
unfortunately not free software.

1: solve ( a*x^2 + b*x + c , x );

~                  2
~       - 4*a*c + b   0.5
~    (---------------)    - 0.5*b
~            4
{x=------------------------------,
~                 a

~                     2
~          - 4*a*c + b   0.5
~     - (---------------)    - 0.5*b
~               4
~ x=---------------------------------}
~                   a



- --
Geraint Bevan
http://homepage.ntlworld.com/geraint.bevan

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