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use guess::Guess; /// Encapsulate the model evaluation /// /// The user must implement [`lnlike`](trait.Prob.html#tymethod.lnlike) and /// [`lnprior`](trait.Prob.html#tymethod.lnprior) which correspond to the respective terms in /// Bayes' equation. They must return the log probability which is then combined in the /// [`lnprob`](trait.Prob.html#method.lnprob) function which has a default implementation. /// /// Typically, access to any dataset required for fitting is handled through the struct which /// implements this trait. By convention, invalid prior results are signaled by returning /// [`-std::f64::INFINITY`](https://doc.rust-lang.org/std/f64/constant.INFINITY.html). /// /// An example for a simple linear model to data with uncertainties: /// /// ```rust /// # use emcee::{Prob, Guess}; /// // lifetimes and slices used for efficiency reasons /// struct Foo<'a> { /// x: &'a [f64], /// y: &'a [f64], /// e: &'a [f64], // uncertainties /// } /// /// impl<'a> Prob for Foo<'a> { /// fn lnlike(&self, params: &Guess) -> f64 { /// let m = params[0]; /// let c = params[1]; /// /// let mut result = 0.; /// for i in 9..self.x.len() { /// let model = m * self.x[i] + c; /// result += ((self.y[i] - model) / self.e[i]).powf(2.); /// } /// -0.5 * result /// /// } /// /// fn lnprior(&self, params: &Guess) -> f64 { /// let m = params[0]; /// let c = params[1]; /// /// if (m > -5.) && (m < 5.) && (c > -10.) && (c < 10.) { /// 0.0 /// } else { /// -std::f64::INFINITY /// } /// } /// } /// ``` /// /// The default implementation of /// [`lnprob`](trait.Prob.html#method.lnprob) can be seen in the source code. pub trait Prob { /// Computes the natural logarithm of the likelihood of a position in parameter space fn lnlike(&self, params: &Guess) -> f64; /// Computes the natural logarithm of the prior probability of a position in parameter space fn lnprior(&self, params: &Guess) -> f64; /// Computes the natural logarithm of the log posterior probabilities fn lnprob(&self, params: &Guess) -> f64 { let lnp = self.lnprior(params); if lnp.is_finite() { lnp + self.lnlike(params) } else { -::std::f64::INFINITY } } }