[Scilab-users] root calculation

[michael.baudin at contrib.scilab.org]

Hi,

This is a nonlinear equation, for which we are searching a zero.

The fsolve function is designed for this purpose:

http://help.scilab.org/fsolve

Notice that there might not be a solution. This is why the algorithm is 
an optimization problem, where the square norm of f(x) is minimized. 
This method also works for a system of nonlinear equations, so that this 
is (much) more general than dichotomy, secant, Brent, etc... which are 
one-variable solvers.

No 1-variable method is available at the Scilab level, to my knowledge. 
But the Brent method is used internally in the computation of the 
inverse Cumulated Distribution Function (quantile) by the DCDFLIB 
library (e.g. X=cdfnor("X",Mean,Std,P,Q)). Notice that Matlab has the 
fzero function :

http://www.mathworks.fr/fr/help/matlab/ref/fzero.html

which uses Brent's method.
But this method is not available directy in Scilab. This is a good 
design choice in my opinion, since fsolve is much more general. But I 
guess that fzero may be faster and more robust, in some cases.

Best regards,

Michaël

Le 2012-11-05 13:13, Paul Carrico a écrit :
> Dear all,
>
> This a stupid question, but how can I solve directly in, Scilab an
> equation such as :
>
> 0.403*X^(-0.121) + 60.5*X^(-0.73) - 0.1839 = 0
>
> ?
>
> Is-it necessary to code a function ? from memory : dichotomy method,
> secant method, Brent one etc. …
>
> Regards
>
> Paul
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