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4.4.6  fsolve or nSolve with the option steffenson_solver

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 xi and the convergence acceleration gives the Steffenson sequence

Ri =xi − 
(xi+1 − xi)2
 (xi+2 − 2 xi+1 + xi)
 

Input :

fsolve(cos(x)=x,x,0,steffenson_solver)

Output :

0.739085133215

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