sparse.sandbox
– Sparse Op Sandbox¶
API¶
Convolutionlike operations with sparse matrix multiplication.
To read about different sparse formats, see U{http://wwwusers.cs.umn.edu/~saad/software/SPARSKIT/paper.ps}.
@todo: Automatic methods for determining best sparse format?

class
theano.sparse.sandbox.sp.
ConvolutionIndices
(use_c_code='/usr/bin/g++')[source]¶ Build indices for a sparse CSC matrix that could implement A (convolve) B.
This generates a sparse matrix M, which generates a stack of image patches when computing the dot product of M with image patch. Convolution is then simply the dot product of (img x M) and the kernels.
static
evaluate
(inshp, kshp, strides=(1, 1), nkern=1, mode='valid', ws=True)[source]¶ Build a sparse matrix which can be used for performing... * convolution: in this case, the dot product of this matrix with the input images will generate a stack of images patches. Convolution is then a tensordot operation of the filters and the patch stack. * sparse local connections: in this case, the sparse matrix allows us to operate the weight matrix as if it were fullyconnected. The structureddot with the input image gives the output for the following layer.
Parameters:  ker_shape – shape of kernel to apply (smaller than image)
 img_shape – shape of input images
 mode – ‘valid’ generates output only when kernel and image overlap overlap fully. Convolution obtained by zeropadding the input
 ws – must be always True
 (dx,dy) – offset parameter. In the case of no weight sharing, gives the pixel offset between two receptive fields. With weight sharing gives the offset between the topleft pixels of the generated patches
Return type: tuple(indices, indptr, logical_shape, sp_type, out_img_shp)
Returns: the structure of a sparse matrix, and the logical dimensions of the image which will be the result of filtering.

static

theano.sparse.sandbox.sp.
convolve
(kerns, kshp, nkern, images, imgshp, step=(1, 1), bias=None, mode='valid', flatten=True)[source]¶ Convolution implementation by sparse matrix multiplication.
Note: For best speed, put the matrix which you expect to be smaller as the ‘kernel’ argument “images” is assumed to be a matrix of shape batch_size x img_size, where the second dimension represents each image in raster order
If flatten is “False”, the output feature map will have shape:
batch_size x number of kernels x output_size
If flatten is “True”, the output feature map will have shape:
batch_size x number of kernels * output_size
Note
IMPORTANT: note that this means that each feature map (image generate by each kernel) is contiguous in memory. The memory layout will therefore be: [ <feature_map_0> <feature_map_1> ... <feature_map_n>], where <feature_map> represents a “feature map” in raster order
kerns is a 2D tensor of shape nkern x N.prod(kshp)
Parameters:  kerns – 2D tensor containing kernels which are applied at every pixel
 kshp – tuple containing actual dimensions of kernel (not symbolic)
 nkern – number of kernels/filters to apply. nkern=1 will apply one common filter to all input pixels
 images – tensor containing images on which to apply convolution
 imgshp – tuple containing image dimensions
 step – determines number of pixels between adjacent receptive fields (tuple containing dx,dy values)
 mode – ‘full’, ‘valid’ see CSM.evaluate function for details
 sumdims – dimensions over which to sum for the tensordot operation. By default ((2,),(1,)) assumes kerns is a nkern x kernsize matrix and images is a batchsize x imgsize matrix containing flattened images in raster order
 flatten – flatten the last 2 dimensions of the output. By default, instead of generating a batchsize x outsize x nkern tensor, will flatten to batchsize x outsize*nkern
Returns: out1, symbolic result
Returns: out2, logical shape of the output img (nkern,heigt,width)
TODO: test for 1D and think of how to do nd convolutions

theano.sparse.sandbox.sp.
max_pool
(images, imgshp, maxpoolshp)[source]¶ Implements a max pooling layer
Takes as input a 2D tensor of shape batch_size x img_size and performs max pooling. Max pooling downsamples by taking the max value in a given area, here defined by maxpoolshp. Outputs a 2D tensor of shape batch_size x output_size.
Parameters:  images – 2D tensor containing images on which to apply convolution. Assumed to be of shape batch_size x img_size
 imgshp – tuple containing image dimensions
 maxpoolshp – tuple containing shape of area to max pool over
Returns: out1, symbolic result (2D tensor)
Returns: out2, logical shape of the output

class
theano.sparse.sandbox.sp2.
Binomial
(format, dtype)[source]¶ Return a sparse matrix having random values from a binomial density having number of experiment n and probability of succes p.
WARNING: This Op is NOT deterministic, as calling it twice with the same inputs will NOT give the same result. This is a violation of Theano’s contract for Ops
Parameters:  n – Tensor scalar representing the number of experiment.
 p – Tensor scalar representing the probability of success.
 shape – Tensor vector for the output shape.
Returns: A sparse matrix of integers representing the number of success.

class
theano.sparse.sandbox.sp2.
Multinomial
(use_c_code='/usr/bin/g++')[source]¶ Return a sparse matrix having random values from a multinomial density having number of experiment n and probability of succes p.
WARNING: This Op is NOT deterministic, as calling it twice with the same inputs will NOT give the same result. This is a violation of Theano’s contract for Ops
Parameters:  n – Tensor type vector or scalar representing the number of experiment for each row. If n is a scalar, it will be used for each row.
 p – Sparse matrix of probability where each row is a probability vector representing the probability of succes. N.B. Each row must sum to one.
Returns: A sparse matrix of random integers from a multinomial density for each row.
Note: It will works only if p have csr format.

class
theano.sparse.sandbox.sp2.
Poisson
(use_c_code='/usr/bin/g++')[source]¶ Return a sparse having random values from a Poisson density with mean from the input.
WARNING: This Op is NOT deterministic, as calling it twice with the same inputs will NOT give the same result. This is a violation of Theano’s contract for Ops
Parameters: x – Sparse matrix. Returns: A sparse matrix of random integers of a Poisson density with mean of x element wise.