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pytensor
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b1b0e8e1
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b1b0e8e1
authored
4月 07, 2015
作者:
Sina Honari
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updating the faq.txt
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doc/tutorial/faq.txt
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b1b0e8e1
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@@ -7,16 +7,16 @@ How to update a subset of weights?
==================================
If you want to update only a subset of a weight matrix (such as
some rows or some columns) that are used in the forward propogation
of
this
iteration, then the cost function should be defined in a way
that it only depends on the subset of weights that are used in th
is
of
each
iteration, then the cost function should be defined in a way
that it only depends on the subset of weights that are used in th
at
iteration.
For example if you want to learn a lookup table, e.g. used for
word embeddings, where each row is a vector of weights representing
the embedding that the model has learned for a word, in each
iteration only the rows of the matrix should get updated that their
corresponding words were used in the forward propogation. Here is
how the theano function
should be written:
the embedding that the model has learned for a word, in each
iteration,
the only rows that should get updated are those containing embeddings
used during the forward propagation. Here is how the theano function
should be written:
>>> # defining a shared variable for the lookup table
>>> lookup_table = theano.shared(matrix_ndarray).
...
...
@@ -24,10 +24,10 @@ how the theano function should be written:
>>> # getting a subset of the table (some rows
>>> # or some columns) by passing an integer vector of
>>> # indices corresponding to those rows or columns.
>>> slice = lookup_table[vector_of_ind
e
ces]
>>> slice = lookup_table[vector_of_ind
i
ces]
>>>
>>> # From now on, use only 'slice'.
>>> # Do not call lookup_table[vector_of_ind
e
ces] again.
>>> # Do not call lookup_table[vector_of_ind
i
ces] again.
>>> # This causes problems with grad as this will create new variables.
>>>
>>> # defining cost which depends only on slice
...
...
@@ -47,8 +47,8 @@ how the theano function should be written:
>>> # Note that currently we just cover the case here,
>>> # not if you use inc_subtensor or set_subtensor with other types of indexing.
>>>
>>> #defining the theano function
>>> f=theano.function(..., update=updates)
>>> #
defining the theano function
>>> f=theano.function(..., update
s
=updates)
Note that you can compute the gradient of the cost function w.r.t.
the entire lookup_table, and the gradient will have nonzero rows only
...
...
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