tracel-ai/burn · error

top_k must be non-zero

Error message

top_k must be non-zero

What it means

Config validation in `FBetaScore`/`ClassificationMetricConfig` construction: the `top_k` argument passed to the multiclass (or related) constructor is zero, which would make top-k classification undefined; config building panics.

Source

Thrown at crates/burn-train/src/metric/fbetascore.rs:74

                ..Default::default()
            },
            beta,
        )
    }

    /// F-beta score metric for multiclass classification.
    ///
    /// # Arguments
    ///
    /// * `beta` - Positive real factor to weight recall's importance.
    /// * `top_k` - The number of highest predictions considered to find the correct label (typically `1`).
    /// * `class_reduction` - [Class reduction](ClassReduction) type.
    #[allow(dead_code)]
    pub fn multiclass(beta: f64, top_k: usize, class_reduction: ClassReduction) -> Self {
        Self::new(
            ClassificationMetricConfig {
                decision_rule: DecisionRule::TopK(
                    NonZeroUsize::new(top_k).expect("top_k must be non-zero"),
                ),
                class_reduction,
            },
            beta,
        )
    }

    /// F-beta score metric for multi-label classification.
    ///
    /// # Arguments
    ///
    /// * `beta` - Positive real factor to weight recall's importance.
    /// * `threshold` - The threshold to transform a probability into a binary prediction.
    /// * `class_reduction` - [Class reduction](ClassReduction) type.
    #[allow(dead_code)]
    pub fn multilabel(beta: f64, threshold: f64, class_reduction: ClassReduction) -> Self {
        Self::new(
            ClassificationMetricConfig {

View on GitHub (pinned to d16f7ba2ed)

Solutions

1. Pass top_k >= 1 (typically 1)
2. Validate user-provided top_k before constructing the metric
3. Use the binary/threshold variant if top-k is not needed

When it happens

Trigger: Thrown at crates/burn-train/src/metric/fbetascore.rs:74 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of tracel-ai/burn@d16f7ba2ed (2026-09-05). Data as JSON: /api/errors/9a15d056924c53e5. Report an issue: GitHub.