MPSCNNPoolingMaxGradient(3)				 MetalPerformanceShaders.framework			       MPSCNNPoolingMaxGradient(3)

NAME

       MPSCNNPoolingMaxGradient

SYNOPSIS

       #import <MPSCNNPooling.h>

       Inherits MPSCNNPoolingGradient.

   Instance Methods
       (nonnull instancetype) - initWithDevice:kernelWidth:kernelHeight:strideInPixelsX:strideInPixelsY:
       (nullable instancetype) - initWithCoder:device:

   Additional Inherited Members
Detailed Description
       This depends on Metal.framework	Specifies the filter for computing the gradient of the max pooling filter. The operation backpropagates a
       gradient vector using chain rule.

       Dilated Max pooling forward pass is defined as:

       out(x) = max_{dx in Window(x)} in(s*x+D*dx), where

       the pooling window definition 'Window(x)' follows MPSCNNPooling specification, 's' is the pixel stride and in() is the source input image
       and D is the dilation factor. For MPSCNNPoolingMaxGradient the dilationRate 'D' is one. NOTE: For even-sized pooling windows with dilation
       rate greater than one the effective pooling window is centered around s*x with non-even windows leaning towards top-left corner. For
       example if kernel width = 2, dilation rate = 3, then the pooling considers positions '-2' and '+1' relative to the pooling window center
       's*x'.

       Hence the partial derivative of the output value wrt. to the input value needed in the gradient backpropagation in MPSCNNPoolingGradient
       is:

       d out(x)/d in(y) = delta_{x_m, y}, where

       delta_{x,y} is the Kronecker delta symbol (see MPSCNNPoolingAverageGradient) and x_m is the index of the maximum value in the corresponding
       pooling window.

       In practice this means that the gradient value for the destination image at pixel 'x' is the sum over these contributions coming from all
       pooling windows that contribute to the max pooling computation in the forward pass, multiplied by the input gradient value in the source
       area of the corresponding pooling window. If there are multiple maximal values within a single pooling window one of them is picked for the
       gradient and this decision is implementation specific, which means that it can vary between different architectures and even between
       different filter parameters.

       Note: The gradient max pooling needs the secondary input image in order to compute the indices of maximal values for each pooling window,
       but this means redundant computations. Later we may add encode calls to MPSCNNPoolingMax that produce a state that contains the coordinates
       of the maximal values to be consumed by the gradient filters.

Method Documentation
   - (nullable instancetype) initWithCoder: (NSCoder *__nonnull) aDecoder(nonnull id< MTLDevice >) device
       NSSecureCoding compatability  See MPSKernel::initWithCoder.

       Parameters:
	   aDecoder The NSCoder subclass with your serialized MPSCNNPoolingMaxGradient
	   device The MTLDevice on which to make the MPSCNNPoolingMaxGradient

       Returns:
	   A new MPSCNNPoolingMaxGradient object, or nil if failure.

       Reimplemented from MPSCNNPoolingGradient.

   - (nonnull instancetype) initWithDevice: (nonnull id< MTLDevice >) device(NSUInteger) kernelWidth(NSUInteger) kernelHeight(NSUInteger)
       strideInPixelsX(NSUInteger) strideInPixelsY
       Initialize a gradient max pooling filter

       Parameters:
	   device The device the filter will run on
	   kernelWidth The width of the kernel. Can be an odd or even value.
	   kernelHeight The height of the kernel. Can be an odd or even value.
	   strideInPixelsX The input stride (upsampling factor) in the x dimension.
	   strideInPixelsY The input stride (upsampling factor) in the y dimension.

       Returns:
	   A valid MPSCNNPoolingGradient object or nil, if failure.

       Reimplemented from MPSCNNPoolingGradient.

Author
       Generated automatically by Doxygen for MetalPerformanceShaders.framework from the source code.

Version MetalPerformanceShaders-100				  Thu Feb 8 2018				       MPSCNNPoolingMaxGradient(3)