This is an implementation of the Dixon-Coles model for estimating soccer teams' strength from goals scored and conceded:

Dixon, Mark J., and Stuart G. Coles. "Modelling association football scores and inefficiencies in the football betting market." Journal of the Royal Statistical Society: Series C (Applied Statistics) 46, no. 2 (1997): 265-280.

By specifying the model as a pair of formulas, it allows the user to estimate the effect of parameters beyond team strength.

dixoncoles_ext(f1, f2, weights, data, init = NULL, ...)

f1 | A formula describing the model for home goals. |
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f2 | A formula describing the model for away goals. |

weights | A formula describing an expression to calculate the weight for each game. |

data | Data frame, list or environment (or object coercible by `as.data.frame` to a data frame) containing the variables in the model. |

init | Initial parameter values. If it is `NULL`, 0 is used for all values. |

... | Arguments passed onto `optim`. |

A list with component `par` containing the best set of parameters found. See `optim` for details.