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  "documentType" : "symbol",
  "framework" : "Accelerate",
  "identifier" : "/documentation/Accelerate/BNNS/ReductionLayer/applyBackward(batchSize:input:output:outputGradient:generatingInputGradient:generatingWeightsGradient:)",
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# applyBackward(batchSize:input:output:outputGradient:generatingInputGradient:generatingWeightsGradient:)

Applies the layer backward to generate input gradients.

```
func applyBackward(batchSize: Int, input: BNNSNDArrayDescriptor, output: BNNSNDArrayDescriptor, outputGradient: BNNSNDArrayDescriptor, generatingInputGradient inputGradient: BNNSNDArrayDescriptor, generatingWeightsGradient weightsGradient: BNNSNDArrayDescriptor? = nil) throws
```

## Parameters

`batchSize`

The number of input-output pairs.

`input`

The descriptor of the input.

`output`

The descriptor of the output.

`outputGradient`

The descriptor of the output gradient.

`inputGradient`

The descriptor of the input gradient.

`weightsGradient`

The descriptor of the weights gradient.

---

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