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fix(distribution): enforce finite params in Gamma::new #333

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fix(distribution): enforce finite params in Gamma::new #333

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f50b0e1
fix(distribution): enforce finite params in Gamma::new
oOOo-YKS Mar 19, 2025
1a8e2fc
fix(gamma): enforce finite params and cleanup validation
oOOo-YKS Apr 5, 2025
969135a
Merge branch 'master' into fix/gamma-param-validation
YeungOnion Jul 18, 2025
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51 changes: 21 additions & 30 deletions src/distribution/gamma.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,18 +33,20 @@ pub enum GammaError {

/// The rate is NaN, zero or less than zero.
RateInvalid,

/// The shape and rate are both infinite.
ShapeAndRateInfinite,
}

impl core::fmt::Display for GammaError {
#[cfg_attr(coverage_nightly, coverage(off))]
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
match self {
GammaError::ShapeInvalid => write!(f, "Shape is NaN zero, or less than zero."),
GammaError::RateInvalid => write!(f, "Rate is NaN zero, or less than zero."),
GammaError::ShapeAndRateInfinite => write!(f, "Shape and rate are infinite"),
GammaError::ShapeInvalid => write!(
f,
"Shape must be finite (not NaN, infinite, zero, or negative)."
),
GammaError::RateInvalid => write!(
f,
"Rate must be finite (not NaN, infinite, zero, or negative)."
),
}
}
}
Expand All @@ -69,22 +71,27 @@ impl Gamma {
/// let mut result = Gamma::new(3.0, 1.0);
/// assert!(result.is_ok());
///
/// result = Gamma::new(0.0, 0.0);
/// result = Gamma::new(1.0, 0.0);
/// assert!(result.is_err());
///
/// result = Gamma::new(0.0, 1.0);
/// assert!(result.is_err());
///
/// result = Gamma::new(f64::INFINITY, 1.0);
/// assert!(result.is_err());
///
/// result = Gamma::new(1.0, f64::INFINITY);
/// assert!(result.is_err());
/// ```
pub fn new(shape: f64, rate: f64) -> Result<Gamma, GammaError> {
if shape.is_nan() || shape <= 0.0 {
if shape.is_nan() || shape <= 0.0 || shape.is_infinite() {
return Err(GammaError::ShapeInvalid);
}

if rate.is_nan() || rate <= 0.0 {
if rate.is_nan() || rate <= 0.0 || rate.is_infinite() {
return Err(GammaError::RateInvalid);
}

if shape.is_infinite() && rate.is_infinite() {
return Err(GammaError::ShapeAndRateInfinite);
}

Ok(Gamma { shape, rate })
}

Expand Down Expand Up @@ -147,12 +154,6 @@ impl ContinuousCDF<f64, f64> for Gamma {
fn cdf(&self, x: f64) -> f64 {
if x <= 0.0 {
0.0
} else if prec::ulps_eq!(x, self.shape) && self.rate.is_infinite() {
1.0
} else if self.rate.is_infinite() {
0.0
} else if x.is_infinite() {
1.0
} else {
gamma::gamma_lr(self.shape, x * self.rate)
}
Expand All @@ -172,12 +173,6 @@ impl ContinuousCDF<f64, f64> for Gamma {
fn sf(&self, x: f64) -> f64 {
if x <= 0.0 {
1.0
} else if prec::ulps_eq!(x, self.shape) && self.rate.is_infinite() {
0.0
} else if self.rate.is_infinite() {
1.0
} else if x.is_infinite() {
0.0
} else {
gamma::gamma_ur(self.shape, x * self.rate)
}
Expand Down Expand Up @@ -468,11 +463,7 @@ mod tests {
(-1.0, 1.0, GammaError::ShapeInvalid),
(-1.0, -1.0, GammaError::ShapeInvalid),
(-1.0, f64::NAN, GammaError::ShapeInvalid),
(
f64::INFINITY,
f64::INFINITY,
GammaError::ShapeAndRateInfinite,
),
(f64::INFINITY, f64::INFINITY, GammaError::ShapeInvalid),
];
for (s, r, err) in invalid {
test_create_err(s, r, err);
Expand Down