*Last updated: 2023-03-16.*
# tf_quant_finance.math.segment_ops.segment_cumsum
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Computes cumulative sum of elements in a segment.
```python
tf_quant_finance.math.segment_ops.segment_cumsum(
x, segment_ids, exclusive=False, dtype=None, name=None
)
```
For a complete description of segment_* ops see documentation of
`tf.segment_sum`. This op extends the `tf.math.cumsum` functionality to
segmented inputs.
The behaviour of this op is the same as that of the op `tf.math.cumsum` within
each segment. The result is effectively a concatenation of the results of
`tf.math.cumsum` applied to each segment with the same interpretation for the
argument `exclusive`.
#### Example
```python
x = tf.constant([2, 5, 1, 7, 9] + [32, 10, 12, 3] + [4, 8, 5])
segments = tf.constant([0, 0, 0, 0, 0] + [1, 1, 1, 1] + [2, 2, 2])
# Inclusive cumulative sum.
# Expected result: [2, 7, 8, 15, 24, 32, 42, 54, 57, 4, 12, 17]
cumsum1 = segment_cumsum(
x, segment_ids=segments, exclusive=False)
# Exclusive cumsum.
# Expected result: [0, 2, 7, 8, 15, 0, 32, 42, 54, 0, 4, 12]
cumsum2 = segment_cumsum(
x, segment_ids=segments, exclusive=True)
```
#### Args:
* `x`: A rank 1 `Tensor` of any dtype for which arithmetic operations are
permitted.
* `segment_ids`: A `Tensor`. Must be one of the following types: int32, int64. A
1-D tensor whose size is equal to the size of `x`. Values should be sorted
and can be repeated. Values must range from `0` to `num segments - 1`.
* `exclusive`: Python bool. See description above.
Default value: False
* `dtype`: Optional `tf.Dtype`. If supplied, the dtype for `x` to use when
converting to `Tensor`.
Default value: None which maps to the default dtype inferred by TF.
* `name`: Python `str` name prefixed to Ops created by this class.
Default value: None which is mapped to the default name 'segment_cumsum'.
#### Returns:
* `cumsums`: A `Tensor` of the same dtype as `x`. Assuming that each segment is
of length greater than or equal to order, if `exclusive` is True,
then the size is `n-order*k` where `n` is the size of x,
`k` is the number of different segment ids supplied if `segment_ids` is
not None or 1 if `segment_ids` is None. If any of the segments is of
length less than the order, then the size is:
`n-sum(min(order, length(segment_j)), j)` where the sum is over segments.
If `exclusive` is False, then the size is `n`.