# Auc¶

class paddle.metric. Auc ( curve='ROC', num_thresholds=4095, name='auc', *args, **kwargs ) [source]

The auc metric is for binary classification. Refer to https://en.wikipedia.org/wiki/Receiver_operating_characteristic#Area_under_the_curve. Please notice that the auc metric is implemented with python, which may be a little bit slow.

The auc function creates four local variables, true_positives, true_negatives, false_positives and false_negatives that are used to compute the AUC. To discretize the AUC curve, a linearly spaced set of thresholds is used to compute pairs of recall and precision values. The area under the ROC-curve is therefore computed using the height of the recall values by the false positive rate, while the area under the PR-curve is the computed using the height of the precision values by the recall.

Parameters
• curve (str) – Specifies the mode of the curve to be computed, ‘ROC’ or ‘PR’ for the Precision-Recall-curve. Default is ‘ROC’.

• num_thresholds (int) – The number of thresholds to use when discretizing the roc curve. Default is 4095. ‘ROC’ or ‘PR’ for the Precision-Recall-curve. Default is ‘ROC’.

• name (str, optional) – String name of the metric instance. Default is auc.

“NOTE: only implement the ROC curve type via Python now.”

Examples

```>>> import numpy as np

>>> n = 8
>>> class0_preds = np.random.random(size = (n, 1))
>>> class1_preds = 1 - class0_preds

>>> preds = np.concatenate((class0_preds, class1_preds), axis=1)
>>> labels = np.random.randint(2, size = (n, 1))

>>> m.update(preds=preds, labels=labels)
>>> res = m.accumulate()
```
```>>> import numpy as np

...     def __init__(self):
...         super().__init__()
...         self.n = 1024
...         self.x = np.random.randn(self.n, 10).astype('float32')
...         self.y = np.random.randint(2, size=(self.n, 1)).astype('int64')
...
...     def __getitem__(self, idx):
...         return self.x[idx], self.y[idx]
...
...     def __len__(self):
...         return self.n
...
...     nn.Linear(10, 2), nn.Softmax())
... )
...     learning_rate=0.001, parameters=model.parameters())
...
>>> def loss(x, y):
...
>>> model.prepare(
...     optim,
...     loss=loss,
>>> data = Data()
>>> model.fit(data, batch_size=16)
```
update ( preds, labels )

Update the auc curve with the given predictions and labels.

Parameters
• preds (numpy.array) – An numpy array in the shape of (batch_size, 2), preds[i][j] denotes the probability of classifying the instance i into the class j.

• labels (numpy.array) – an numpy array in the shape of (batch_size, 1), labels[i] is either o or 1, representing the label of the instance i.

accumulate ( )

Return the area (a float score) under auc curve

Returns

the area under auc curve

Return type

float

reset ( )

Reset states and result

name ( )

Returns metric name

compute ( *args )

This API is advanced usage to accelerate metric calculating, calculations from outputs of model to the states which should be updated by Metric can be defined here, where Paddle OPs is also supported. Outputs of this API will be the inputs of “Metric.update”.

If `compute` is defined, it will be called with outputs of model and labels from data as arguments, all outputs and labels will be concatenated and flatten and each filed as a separate argument as follows: `compute(output1, output2, ..., label1, label2,...)`

If `compute` is not defined, default behaviour is to pass input to output, so output format will be: `return output1, output2, ..., label1, label2,...`

see `Metric.update`