Binarymatthewscorrcoef

---
name: binarymatthewscorrcoef
description: Compute the BinaryMatthewsCorrCoef metric — provided by torchmetrics. Use when the user has predictions and ground-truth and needs to compute BinaryMatthewsCorrCoef, or asks how to score with BinaryMatthewsCorrCoef.
metadata:
  skill_kind: metric
  source_lib: torchmetrics
  import_path: torchmetrics.classification.BinaryMatthewsCorrCoef
  source: library_introspection
---

# binarymatthewscorrcoef

> Metric `BinaryMatthewsCorrCoef` from `torchmetrics` (torchmetrics.classification.BinaryMatthewsCorrCoef)

## When to invoke this skill

The user has predictions + ground truth and asks to evaluate with BinaryMatthewsCorrCoef, or
mentions `torchmetrics.classification.BinaryMatthewsCorrCoef` directly, or wants the standard torchmetrics implementation.

## Reference signature

```python
from torchmetrics.classification import BinaryMatthewsCorrCoef

# BinaryMatthewsCorrCoef(threshold: float = 0.5, ignore_index: Optional[int] = None, validate_args: bool = True, **kwargs: Any) -> None
```

## Library docstring

```
Calculate `Matthews correlation coefficient`_ for binary tasks.

This metric measures the general correlation or quality of a classification.

As input to ``forward`` and ``update`` the metric accepts the following input:

- ``preds`` (:class:`~torch.Tensor`): A int tensor or float tensor of shape ``(N, ...)``. If preds is a floating
  point tensor with values outside [0,1] range we consider the input to be logits and will auto apply sigmoid
  per element. Additionally, we convert to int tensor with thresholding using the value in ``threshold``.
- ``target`` (:class:`~torch.Tensor`): An int tensor of shape ``(N, ...)``

.. tip::
   Additional dimension ``...`` will be flattened into the batch dimension.

As output to ``forward`` and ``compute`` the metric returns the following output:

- ``bmcc`` (:class:`~torch.Tensor`): A tensor containing the Binary Matthews Correlation Coefficient.

Args:
    threshold: Threshold for transforming probability to binary (0,1) predictions
    ignore_index:
        Specifies a target value that is ignored and does not contribute to the metric calculation
    validate_args: bool indicating if input arguments and tensors should be validated for correctness.
        Set to ``False`` for faster computations.
    kwargs: Additional keyword arguments, see :ref:`Metric kwargs` for more info.

Example (preds is int tensor):
    >>> from torch import tensor
    >>> from torchmetrics.classification import BinaryMatthewsCorrCoef
    >>> target = tensor([1, 1, 0, 0])
    >>> preds = tensor([0, 1, 0, 0])
    >>> metric = BinaryMatthewsCorrCoef()
    >>> metric(preds, target)
    tensor(0.5774)

Example (preds is float tensor):
    >>> from torchmetrics.classification import BinaryMatthewsCorrCoef
    >>> target = tensor([1, 1, 0, 0])
    >>> preds = tensor([0.35, 0.85, 0.48, 0.01])
    >>> metric = BinaryMatthewsCorrCoef()
    >>> metric(preds, target)
    tensor(0.5774)
```

## Quick recipe

```python
import torchmetrics.classification as _m
score = _m.BinaryMatthewsCorrCoef(y_true, y_pred)
```

## Don'ts

- Don't reimplement when the library version handles edge cases (NaN, ties, empty inputs) better than a hand-rolled formula.
- Always check the library version's argument order — sklearn is `(y_true, y_pred)` while torchmetrics is `(preds, target)`.