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  "identifier" : "/documentation/Accelerate/BNNSLayerParametersLSTM/input_descriptor",
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# input_descriptor

Descriptors of the input, hidden input, and cell-state input data.

```
var input_descriptor: BNNSLSTMDataDescriptor
```

## Discussion

You must define the layout of this descriptor as one of either:

- [`BNNSDataLayoutSNE`](/documentation/Accelerate/BNNSDataLayoutSNE) with the shape ([`input_size`](/documentation/Accelerate/BNNSLayerParametersLSTM/input_size),[`batch_size`](/documentation/Accelerate/BNNSLayerParametersLSTM/batch_size),[`seq_len`](/documentation/Accelerate/BNNSLayerParametersLSTM/seq_len))
- [`BNNSDataLayoutNSE`](/documentation/Accelerate/BNNSDataLayoutNSE) with the shape  ([`input_size`](/documentation/Accelerate/BNNSLayerParametersLSTM/input_size),[`seq_len`](/documentation/Accelerate/BNNSLayerParametersLSTM/seq_len),[`batch_size`](/documentation/Accelerate/BNNSLayerParametersLSTM/batch_size))

If you don’t specify a layout, BNNS uses [`BNNSDataLayoutSNE`](/documentation/Accelerate/BNNSDataLayoutSNE).

Use C style multidimensional array notation to define the hierarchy of the [`hidden_desc`](/documentation/Accelerate/BNNSLSTMDataDescriptor/hidden_desc) and [`cell_state_desc`](/documentation/Accelerate/BNNSLSTMDataDescriptor/cell_state_desc) descriptors as `[num_layers][num_directions][batch_size][hidden_size]`.

If [`lstm_flags`](/documentation/Accelerate/BNNSLayerParametersLSTM/lstm_flags) includes [`BNNSLayerFlagsLSTMBidirectional`](/documentation/Accelerate/BNNSLayerFlagsLSTMBidirectional), BNNS defines `num_directions` as `2`, or otherwise `1`.

If the corresponding data of the [`hidden_desc`](/documentation/Accelerate/BNNSLSTMDataDescriptor/hidden_desc) and [`cell_state_desc`](/documentation/Accelerate/BNNSLSTMDataDescriptor/cell_state_desc) descriptors is `nil`, BNNS treats their [`input_descriptor`](/documentation/Accelerate/BNNSLayerParametersLSTM/input_descriptor) as zero-filled arrays.

---

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