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** monter:** Solve equations with fsolve
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The Steffenson method is generically the fastest method.

It combines the Newton method with a "delta-two" Aitken acceleration :
with the Newton method, we obtain the sequence *x*_{i} and the convergence
acceleration gives the Steffenson sequence

*R*_{i} =

*x*_{i} -

Input :
`fsolve(cos(x)=x,x,0,steffenson_solver)`

Output :
`0.739085133215`

giac documentation written by Renée De Graeve and Bernard Parisse