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# tf.keras.metrics.MeanRelativeError

Computes the mean relative error by normalizing with the given values.

Inherits From: `Mean`, `Metric`, `Layer`, `Module`

This metric creates two local variables, `total` and `count` that are used to compute the mean relative error. This is weighted by `sample_weight`, and it is ultimately returned as `mean_relative_error`: an idempotent operation that simply divides `total` by `count`.

If `sample_weight` is `None`, weights default to 1. Use `sample_weight` of 0 to mask values.

`normalizer` The normalizer values with same shape as predictions.
`name` (Optional) string name of the metric instance.
`dtype` (Optional) data type of the metric result.

#### Standalone usage:

````m = tf.keras.metrics.MeanRelativeError(normalizer=[1, 3, 2, 3])`
`m.update_state([1, 3, 2, 3], [2, 4, 6, 8])`
```
````# metric = mean(|y_pred - y_true| / normalizer)`
`#        = mean([1, 1, 4, 5] / [1, 3, 2, 3]) = mean([1, 1/3, 2, 5/3])`
`#        = 5/4 = 1.25`
`m.result().numpy()`
`1.25`
```

Usage with `compile()` API:

``````model.compile(
optimizer='sgd',
loss='mse',
metrics=[tf.keras.metrics.MeanRelativeError(normalizer=[1, 3])])
``````

## Methods

### `merge_state`

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Merges the state from one or more metrics.

This method can be used by distributed systems to merge the state computed by different metric instances. Typically the state will be stored in the form of the metric's weights. For example, a tf.keras.metrics.Mean metric contains a list of two weight values: a total and a count. If there were two instances of a tf.keras.metrics.Accuracy that each independently aggregated partial state for an overall accuracy calculation, these two metric's states could be combined as follows:

````m1 = tf.keras.metrics.Accuracy()`
`_ = m1.update_state([[1], [2]], [[0], [2]])`
```
````m2 = tf.keras.metrics.Accuracy()`
`_ = m2.update_state([[3], [4]], [[3], [4]])`
```
````m2.merge_state([m1])`
`m2.result().numpy()`
`0.75`
```

Args
`metrics` an iterable of metrics. The metrics must have compatible state.

Raises
`ValueError` If the provided iterable does not contain metrics matching the metric's required specifications.

### `reset_state`

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Resets all of the metric state variables.

This function is called between epochs/steps, when a metric is evaluated during training.

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