The original neural network from Torch7, nn, contains stable and widely used modules. 'nnx' contains more experimental, unproven modules, and optimizations. Modules that become stable and which are proven useful make their way into 'nn' (some already have).

This section includes documentation for the following objects:

• SoftMaxTree : a hierarchical log-softmax Module;
• TreeNLLCriterion : a negative log-likelihood Criterion for the SoftMaxTree;
• CTCCriterion : a Connectionist Temporal Classification Criterion based on warp-ctc;
• PushTable (and PullTable) : extracts a table element and inserts it later in the network;
• MultiSoftMax : performs a softmax over the last dimension of a 2D or 3D input;
• SpatialReSampling : performs bilinear resampling of a 3D or 4D input image;
• [QDRiemaNNLinear] (#nnx.QDRiemaNNLinear) : quasi-diagonal reduction for Riemannian gradient descent
• Recurrent : a generalized recurrent neural network container;

The forward method returns an output Tensor of size 1D, while backward returns a table {gradInput, gradTarget}. The second variable is just a Tensor of zeros , such that the targets can be propagated through Containers like ParallelTable.

> input = torch.randn(5,10)
> target = torch.IntTensor{20,24,27,10,12}
> gradOutput = torch.randn(5)
> root_id = 29
> input_size = 10	
> hierarchy = {
>>    [29]=torch.IntTensor{30,1,2}, [1]=torch.IntTensor{3,4,5}, 
>>    [2]=torch.IntTensor{6,7,8}, [3]=torch.IntTensor{9,10,11},
>>    [4]=torch.IntTensor{12,13,14}, [5]=torch.IntTensor{15,16,17},
>>    [6]=torch.IntTensor{18,19,20}, [7]=torch.IntTensor{21,22,23},
>>    [8]=torch.IntTensor{24,25,26,27,28}
>> }
> smt = nn.SoftMaxTree(input_size, hierarchy, root_id)
> smt:forward{input, target}
-3.5186
-3.8950
-3.7433
-3.3071
-3.0522
[torch.DoubleTensor of dimension 5]
> smt:backward({input, target}, gradOutput)
{
  1 : DoubleTensor - size: 5x10
  2 : IntTensor - size: 5
}

An example utilizing the above SoftMaxTree Module and a Linear Module demonstrates how the PushTable can be used to forward the target Tensor without any other Table Modules:

> mlp = nn.Sequential()
> linear = nn.Linear(50,100)
> push = nn.PushTable(2)
> pull = push:pull(2)
> mlp:add(push)
> mlp:add(nn.SelectTable(1))
> mlp:add(linear)
> mlp:add(pull)
> mlp:add(smt) --smt is a SoftMaxTree instance
> mlp:forward{input, target} -- input and target are defined above
-3.5186
-3.8950
-3.7433
-3.3071
-3.0522
[torch.DoubleTensor of dimension 5]
> mlp:backward({input, target}, gradOutput) -- so is gradOutput
{
  1 : DoubleTensor - size: 5x10
  2 : IntTensor - size: 5
}

The above code is equivalent to the following:

> mlp2 = nn.Sequential()
> para = nn.ParallelTable()
> para:add(linear)
> para:add(nn.Identity())
> mlp2:add(para)
> mlp2:add(smt)
> mlp2:forward{input, target}
-3.5186
-3.8950
-3.7433
-3.3071
-3.0522
[torch.DoubleTensor of dimension 5]
> mlp2:backward({input, target}, gradOutput)
{
  1 : DoubleTensor - size: 5x10
  2 : IntTensor - size: 5
}

In some cases, this can simplify the digraph of Modules. Note that a PushTable can be associated to many PullTables, but each PullTable is associated to only one PushTable.

gives the output:

<a name='nnx.MultiSoftMax'/>
### MultiSoftMax ###
This Module takes 2D or 3D input and performs a softmax over the last dimension. 
It uses the existing [SoftMax](https://github.com/torch/nn/blob/master/doc/transfer.md#nn.SoftMax) 
CUDA/C code to do so such that the Module can be used on both GPU and CPU. 
This can be useful for [keypoint detection](https://github.com/nicholas-leonard/dp/blob/master/doc/facialkeypointstutorial.md#multisoftmax).

<a name='nnx.SpatialReSampling'/>
### SpatialReSampling ###
Applies a 2D re-sampling over an input image composed of
several input planes (or channels, colors). The input tensor in `forward(input)` is 
expected to be a 3D or 4D tensor of size : `[batchSize x] nInputPlane x width x height`. 
The number of output planes will be the same as the number of input
planes.

The re-sampling is done using [bilinear interpolation](http://en.wikipedia.org/wiki/Bilinear_interpolation). 
For a simple nearest-neihbor upsampling, use `nn.SpatialUpSampling()`,
and for a simple average-based down-sampling, use 
`nn.SpatialDownSampling()`.

If the input image is a 3D tensor of size `nInputPlane x height x width`,
the output image size will be `nInputPlane x oheight x owidth` where
`owidth` and `oheight` are given to the constructor.

Instead of `owidth` and `oheight`, one can provide `rwidth` and `rheight`, 
such that `owidth = iwidth*rwidth` and `oheight = iheight*rheight`.

As an example, we can run the following code on the famous Lenna image:
```lua
require 'image'                                                           
require 'nnx'
input = image.loadPNG('doc/image/Lenna.png')
l = nn.SpatialReSampling{owidth=150,oheight=150}
output = l:forward(input)
image.save('doc/image/Lenna-150x150-bilinear.png', output)

• Torch7 (www.torch.ch)

• Install Torch7 (refer to its own documentation).
• clone this project into dev directory of Torch7.
• Rebuild torch, it will include new projects too.

First run torch, and load nnx:

$ torch

> require 'nnx'

Once loaded, tab-completion will help you navigate through the library (note that most function are added directly to nn):

> nnx. + TAB
...
> nn. + TAB

In particular, it's good to verify that all modules provided pass their tests:

> nnx.test_all()
> nnx.test_omp()

DEPRECATED July 6th, 2015. Use rnn instead.