# singleGateRNN(_:recurrentWeight:inputWeight:bias:initState:mask:descriptor:name:) Creates a single-gate RNN operation and returns the value and optionally the training state tensor. ``` func singleGateRNN(_ source: MPSGraphTensor, recurrentWeight: MPSGraphTensor, inputWeight: MPSGraphTensor?, bias: MPSGraphTensor?, initState: MPSGraphTensor?, mask: MPSGraphTensor?, descriptor: MPSGraphSingleGateRNNDescriptor, name: String?) -> [MPSGraphTensor] ``` ## Parameters `source` A tensor that contains the source data `x[t]` with the data layout [T,N,I]. In case `inputWeight = nil` and `bidirectional = NO` then the layout is [T,N,H] and for `inputWeight = nil` and `bidirectional = YES` the layout is [T,N,2H]. `recurrentWeight` A tensor containing the recurrent weights `R`. For `bidirectional` the layout is [2,H,H] and otherwise it is [H,H]. `inputWeight` A tensor containing the input weights matrix `W` - optional, if missing the operation assumes a diagonal unit-matrix. For `bidirectional` the layout is [2H,I] and otherwise it is [H,I]. `bias` A tensor containing the bias `b` - optional, if missing the operation assumes zeroes. For `bidirectional` the layout is [2H] and otherwise it is [H]. `initState` The initial internal state of the RNN `h[-1]` - optional, if missing the operation assumes zeroes. For `bidirectional` the layout is [N,2H] and otherwise it is [N,H]. `mask` A tensor containing the mask `m` - optional, if missing the operation assumes ones. This is useful for dropout support. `descriptor` A descriptor that defines the parameters for the RNN operation. `name` The name for the operation. ## Return Value A valid MPSGraphTensor array of size 1 or 2, depending on value of `descriptor.training`. The layout of the both outputs is [T,N,H] or [T,N,2H] for bidirectional. ## Discussion This operation returns tensors `h` and optionally `z` that are defined recursively as follows: ```md for t = 0 to T-1 z[t] = x[t] W^T + (h[t-1]m) R^T + b h[t] = activation( z[t] ), where ``` `W` is optional `inputWeight`, `R` is `recurrentWeight`, `b` is `bias`, `m` is optional `mask`, `x[t]` is `source` `h[t]` is the first output, `z[t]` is the second output (optional) and `h[-1]` is `initState`. See [`MPSGraphSingleGateRNNDescriptor`](/documentation/MetalPerformanceShadersGraph/MPSGraphSingleGateRNNDescriptor) for different `activation` options. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)