gam 0.3.119

Generalized penalized likelihood engine
Documentation 
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/// Decay law for deterministic Gumbel/concrete assignment temperature.
#[derive(Debug, Clone)]
pub enum ScheduleKind {
    Geometric { rate: f64 },
    Linear { steps: usize },
    ReciprocalIter,
}

/// Outer-state temperature annealing for SAE assignment relaxations.
///
/// Annealing drives the continuous concrete/softmax assignment toward the
/// discrete argmax or IBP active-set solution while PIRLS solves smooth
/// positive-temperature subproblems. In the zero-floor limit, softmax becomes
/// argmax and the IBP-MAP sigmoid active set becomes exact; a positive
/// `tau_min` optimizes the corresponding near-discrete MAP problem.
#[derive(Debug, Clone)]
pub struct GumbelTemperatureSchedule {
    pub tau_start: f64,
    pub tau_min: f64,
    pub decay: ScheduleKind,
    pub iter_count: usize,
}

impl GumbelTemperatureSchedule {
    #[must_use = "build error must be handled"]
    pub fn new(tau_start: f64, tau_min: f64, decay: ScheduleKind) -> Result<Self, String> {
        let sched = Self {
            tau_start,
            tau_min,
            decay,
            iter_count: 0,
        };
        sched.validate()?;
        Ok(sched)
    }

    pub fn validate(&self) -> Result<(), String> {
        if !(self.tau_start.is_finite() && self.tau_start > 0.0) {
            return Err(format!(
                "GumbelTemperatureSchedule: tau_start must be finite and positive; got {}",
                self.tau_start
            ));
        }
        if !(self.tau_min.is_finite() && self.tau_min > 0.0) {
            return Err(format!(
                "GumbelTemperatureSchedule: tau_min must be finite and positive; got {}",
                self.tau_min
            ));
        }
        if self.tau_min > self.tau_start {
            return Err(format!(
                "GumbelTemperatureSchedule: tau_min ({}) cannot exceed tau_start ({})",
                self.tau_min, self.tau_start
            ));
        }
        match self.decay {
            ScheduleKind::Geometric { rate } => {
                if !(rate.is_finite() && rate > 0.0 && rate < 1.0) {
                    return Err(format!(
                        "GumbelTemperatureSchedule::Geometric: rate must be in (0, 1); got {rate}"
                    ));
                }
            }
            ScheduleKind::Linear { steps } => {
                if steps == 0 {
                    return Err("GumbelTemperatureSchedule::Linear: steps must be positive".into());
                }
            }
            ScheduleKind::ReciprocalIter => {}
        }
        Ok(())
    }

    pub fn current_tau(&self, iter: usize) -> f64 {
        let raw = match self.decay {
            ScheduleKind::Geometric { rate } => self.tau_start * rate.powf(iter as f64),
            ScheduleKind::Linear { steps } => {
                if iter >= steps {
                    self.tau_min
                } else {
                    let frac = iter as f64 / steps as f64;
                    self.tau_start + frac * (self.tau_min - self.tau_start)
                }
            }
            ScheduleKind::ReciprocalIter => self.tau_start / (1.0 + iter as f64),
        };
        raw.max(self.tau_min)
    }

    pub fn step(&mut self) -> f64 {
        let tau = self.current_tau(self.iter_count);
        self.iter_count += 1;
        tau
    }
}

#[derive(Debug, Clone, PartialEq)]
pub enum SearchStrategy {
    Fixed,
    ExponentialSweep { values: Vec<f64> },
}

impl SearchStrategy {
    #[must_use]
    pub fn is_fixed(&self) -> bool {
        matches!(self, Self::Fixed)
    }

    #[must_use]
    pub fn sweep_values(&self) -> Option<&[f64]> {
        match self {
            Self::Fixed => None,
            Self::ExponentialSweep { values } => Some(values),
        }
    }
}