# tf.compat.v1.assign_sub

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|---|
| [![](https://www.tensorflow.org/images/GitHub-Mark-32px.png) View source on GitHub](https://github.com/tensorflow/tensorflow/blob/v2.13.1/tensorflow/python/ops/state_ops.py#L132-L201) |

Update `ref` by subtracting `value` from it.

    tf.compat.v1.assign_sub(
        ref, value, use_locking=None, name=None
    )

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## Migrate to TF2

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> [!CAUTION]
> **Caution:** This API was designed for TensorFlow v1. Continue reading for details on how to migrate from this API to a native TensorFlow v2 equivalent. See the [TensorFlow v1 to TensorFlow v2 migration guide](https://www.tensorflow.org/guide/migrate) for instructions on how to migrate the rest of your code.

[`tf.compat.v1.assign_sub`](https://www.tensorflow.org/versions/r2.13/api_docs/python/tf/compat/v1/assign_sub) is mostly compatible with eager
execution and [`tf.function`](https://www.tensorflow.org/versions/r2.13/api_docs/python/tf/function).

To switch to the native TF2 style, one could use method 'assign_sub' of
[`tf.Variable`](https://www.tensorflow.org/versions/r2.13/api_docs/python/tf/Variable):

#### How to Map Arguments

| TF1 Arg Name | TF2 Arg Name | Note |
|---|---|---|
| `ref` | `self` | In `assign_sub()` method |
| `value` | `value` | In `assign_sub()` method |
| `use_locking` | `use_locking` | In `assign_sub()` method |
| `name` | `name` | In `assign_sub()` method |
| - | `read_value` | Set to True to replicate behavior (True is default) |

#### Before \& After Usage Example

Before:

    with tf.Graph().as_default():
      with tf.compat.v1.Session() as sess:
        a = tf.compat.v1.Variable(1, dtype=tf.int64)
        sess.run(a.initializer)
        update_op = tf.compat.v1.assign_sub(a, 1)
        res_a = sess.run(update_op)
        res_a
    0

After:

    b = tf.Variable(1, dtype=tf.int64)
    res_b = b.assign_sub(1)
    res_b.numpy()
    0

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## Description

This operation outputs `ref` after the update is done.
This makes it easier to chain operations that need to use the reset value.
Unlike [`tf.math.subtract`](https://www.tensorflow.org/versions/r2.13/api_docs/python/tf/math/subtract), this op does not broadcast. `ref` and `value`
must have the same shape.

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| ## Args ||
|---|---|
| `ref` | A mutable `Tensor`. Must be one of the following types: `float32`, `float64`, `int64`, `int32`, `uint8`, `uint16`, `int16`, `int8`, `complex64`, `complex128`, `qint8`, `quint8`, `qint32`, `half`. Should be from a `Variable` node. |
| `value` | A `Tensor`. Must have the same shape and dtype as `ref`. The value to be subtracted to the variable. |
| `use_locking` | An optional `bool`. Defaults to `False`. If True, the subtraction will be protected by a lock; otherwise the behavior is undefined, but may exhibit less contention. |
| `name` | A name for the operation (optional). |

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| ## Returns ||
|---|---|
| Same as `ref`. Returned as a convenience for operations that want to use the new value after the variable has been updated. ||

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