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fix: Triangular::pdf returns NaN when mode equals min #460

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fix: Triangular::pdf returns NaN when mode equals min #460

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b9d6f57
fix: Triangular::pdf returns NaN when mode equals min
jaideeppyne Aug 28, 2026
70402ba
Drop the explanatory comments and split out the endpoint tests
jaideeppyne Aug 28, 2026
211756d
Cut the doc note too
jaideeppyne Aug 28, 2026
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25 changes: 24 additions & 1 deletion src/distribution/triangular.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -393,7 +393,11 @@ impl Continuous<f64, f64> for Triangular {
let b = self.max;
let c = self.mode;
if a <= x && x <= c {
2.0 * (x - a) / ((b - a) * (c - a))
if c == a {
2.0 / (b - a)
} else {
2.0 * (x - a) / ((b - a) * (c - a))
}
} else if c < x && x <= b {
2.0 * (b - x) / ((b - a) * (b - c))
} else {
Expand Down Expand Up @@ -549,6 +553,15 @@ mod tests {
test_exact(-5.0, -3.0, -4.0, 0.5, pdf(-3.5));
}

#[test]
fn test_pdf_mode_at_an_endpoint() {
let pdf = |arg: f64| move |x: Triangular| x.pdf(arg);
test_exact(0.0, 1.0, 0.0, 2.0, pdf(0.0));
test_exact(-2.0, 5.0, -2.0, 2.0 / 7.0, pdf(-2.0));
test_exact(0.0, 1.0, 1.0, 2.0, pdf(1.0));
test_exact(-2.0, 5.0, 5.0, 2.0 / 7.0, pdf(5.0));
}

#[test]
fn test_ln_pdf() {
let ln_pdf = |arg: f64| move |x: Triangular| x.ln_pdf(arg);
Expand All @@ -569,6 +582,14 @@ mod tests {
test_exact(-5.0, -3.0, -4.0, 0.5f64.ln(), ln_pdf(-3.5));
}

#[test]
fn test_ln_pdf_mode_at_an_endpoint() {
let ln_pdf = |arg: f64| move |x: Triangular| x.ln_pdf(arg);
test_exact(0.0, 1.0, 0.0, 2f64.ln(), ln_pdf(0.0));
test_exact(-2.0, 5.0, -2.0, (2.0f64 / 7.0).ln(), ln_pdf(-2.0));
test_exact(0.0, 1.0, 1.0, 2f64.ln(), ln_pdf(1.0));
}

#[test]
fn test_cdf() {
let cdf = |arg: f64| move |x: Triangular| x.cdf(arg);
Expand Down Expand Up @@ -640,5 +661,7 @@ mod tests {
fn test_continuous() {
density_util::check_continuous_distribution(&create_ok(-5.0, 5.0, 0.0), -5.0, 5.0);
density_util::check_continuous_distribution(&create_ok(-15.0, -2.0, -3.0), -15.0, -2.0);
density_util::check_continuous_distribution(&create_ok(-5.0, 5.0, -5.0), -5.0, 5.0);
density_util::check_continuous_distribution(&create_ok(-5.0, 5.0, 5.0), -5.0, 5.0);
}
}