# fsolve with the option steffenson_solver

### 10.4.6 fsolve with the option steffenson_solver

The Steffenson method is generically the fastest method. It combines Newton’s method with a "delta-two" Aitken acceleration: with Newton’s method, you get the sequence xi and the convergence acceleration gives the Steffenson sequence

Ri =xi −

(xi+1 − xi)2
(xi+2 − 2 xi+1 + xi)

#### Example.

Input:

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

Output:

0.739085133215