## kernels.fit_mack()


Fit the distribution-free chain ladder on a single-cohort Triangle.


Usage

``` python
kernels.fit_mack(
    triangle, *, loss_field="paid_loss", as_of=None, sigma_rule="mack"
)
```


[as_of](Triangle.as_of.md#ibnr.Triangle.as_of) slices the backtest diagonal first (the training window); the triangle must hold exactly one segment combination. `sigma_rule` selects how the last development step's variance is estimated - see `_estimate_factors`.