# s2Fista

##### Hyper-parameter wrapper for FISTA.

This is a very simple function that supplies the hyper-parameters for the Fast Iterative Soft-Threshold Algorithm (FISTA) that solves the `s2net`

minimization problem.

- Keywords
- optimize

##### Usage

`s2Fista(MAX_ITER_INNER = 5000, TOL = 1e-07, t0 = 2, step = 0.1, use_warmstart = FALSE)`

##### Arguments

- MAX_ITER_INNER
Number of iterations of FISTA

- TOL
The relative tolerance. The algorith stops when the objective does not improve more than

`TOL*`

the null model's objective function evaluation, after two succesive iterations.- t0
The initial stepsize for backtracking.

- step
The scale factor in the stepsize to backtrack until a valid step is found.

- use_warmstart
Should we use a warm

`beta`

to fit the model? This is useful to speed-up hyper-parameter searching methods.

##### Value

Returns an object of S3 class `s2Fista`

with the input arguments as fields.

##### References

Beck, A., & Teboulle, M. (2009).
A fast iterative shrinkage-thresholding algorithm for linear inverse problems. *SIAM journal on imaging sciences*, 2(1), 183-202. 10.1137/080716542

##### See Also

*Documentation reproduced from package s2net, version 1.0, License: GPL (>= 2)*