do not allocate in `x_converged`

[longemen3000]

it changes y = x .- z for an iterator. ideally, a custom struct could be provided for this, i imagine some problems could arise if using CUArrays?

[pkofod]

I suppose preallocating y is an alternative ?

[longemen3000]

it is an alternative. Ideally, there should be a way to calculate norm(dx) without allocating somewhere, but the last time i asked, that was the agreed-upon solution

[pkofod]

tests failed it seems

[pkofod]

ah that was the anderson test

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@8d4792b). Click here to learn what that means. The diff coverage is n/a.

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[ararslan]

Looks like CI passed