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POCreating shared weight connections in Pybrain
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  1. POCreating shared weight connections in Pybrain
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    copied!<p>I am trying to create a neural network in PyBrain which utilizes shared weight connections, but am having trouble doing so. I haven't found too many examples which use these type of connections, but had thought that I had gleaned the way to use them from those that I found and the source code. But apparently I was not so lucky. </p> <p>As a simple example, I'm trying to create the following shared weight neural network: <a href="http://i49.tinypic.com/ztuc2g.jpg" rel="nofollow noreferrer">a simple SWNN http://i49.tinypic.com/ztuc2g.jpg</a></p> <p>The connections shown in rectangles I would like to be shared, in that the weights along each path are the same (swapping the input vector [x,y] with [y,x] should yield the same output). </p> <p>I attempted to build this architecture with the following code:</p> <pre><code>from pybrain.structure.modules.linearlayer import LinearLayer from pybrain.structure.modules.sigmoidlayer import SigmoidLayer from pybrain.structure.moduleslice import ModuleSlice from pybrain.structure.networks.feedforward import FeedForwardNetwork from pybrain.structure.connections.shared import MotherConnection,SharedFullConnection net=FeedForwardNetwork() # make modules inp=LinearLayer(2,name='input') h1=SigmoidLayer(2,name='hidden') outp=LinearLayer(1,name='output') # now add modules net.addOutputModule(outp) net.addInputModule(inp) net.addModule(h1) # now we need to create the connections mc=MotherConnection(2,name='mother') mc2=MotherConnection(2,name='mother2') topInput=ModuleSlice(inp,outSliceFrom=0,outSliceTo=1) bottomInput=ModuleSlice(inp,outSliceFrom=1,outSliceTo=2) topHidden=ModuleSlice(h1,inSliceFrom=0,inSliceTo=1) bottomHidden=ModuleSlice(h1,inSliceFrom=1,inSliceTo=2) net.addConnection(SharedFullConnection(mc,topInput,topHidden)) net.addConnection(SharedFullConnection(mc,bottomInput,bottomHidden)) net.addConnection(SharedFullConnection(mc2,topHidden,outp)) net.addConnection(SharedFullConnection(mc2,bottomHidden,outp)) # finish up net.sortModules() #print net.activate([2,1]) </code></pre> <p>In the above code I created two MotherConnections, mc and mc2, the idea being that these two objects would hold the shared weights in my first and second rectangle, respectively, shown in the figure. I then used ModuleSlice to divvy up the input module and the hidden module into two groups. I then tried to addConnections using the mc and mc2 containers to connect these paths. </p> <p>I do not get an error by running the above code. But if I try to test the network by uncommenting the net.activate statement at the end, I get the following error:</p> <pre><code>Traceback (most recent call last): File "test.py", line 38, in &lt;module&gt; print net.activate([2,1]) File "/usr/local/lib/python2.7/dist-packages/PyBrain-0.3.1-py2.7.egg/pybrain/structure/networks/feedforward.py", line 19, in activate return super(FeedForwardNetworkComponent, self).activate(inpt) File "/usr/local/lib/python2.7/dist-packages/PyBrain-0.3.1- py2.7.egg/pybrain/structure/modules/module.py", line 123, in activate self.forward() File "/usr/local/lib/python2.7/dist-packages/PyBrain-0.3.1-py2.7.egg/pybrain/structure/modules/module.py", line 75, in forward self.outputbuffer[self.offset]) File "/usr/local/lib/python2.7/dist-packages/PyBrain-0.3.1- py2.7.egg/pybrain/structure/networks/feedforward.py", line 32, in _forwardImplementation c.forward() File "/usr/local/lib/python2.7/dist-packages/PyBrain-0.3.1-py2.7.egg/pybrain/structure/connections/connection.py", line 77, in forward self.outmod.inputbuffer[outmodOffset, self.outSliceFrom:self.outSliceTo]) File "/usr/local/lib/python2.7/dist-packages/PyBrain-0.3.1-py2.7.egg/pybrain/structure/connections/shared.py", line 64, in _forwardImplementation FullConnection._forwardImplementation(self, inbuf, outbuf) File "/usr/local/lib/python2.7/dist-packages/PyBrain-0.3.1-py2.7.egg/pybrain/structure/connections/full.py", line 19, in _forwardImplementation outbuf += dot(reshape(self.params, (self.outdim, self.indim)), inbuf) File "/usr/lib/python2.7/dist-packages/numpy/core/fromnumeric.py", line 171, in reshape return reshape(newshape, order=order) ValueError: total size of new array must be unchanged </code></pre> <p>so I imagine I must be misunderstanding something about the way this is set up. Many thanks to anyone who can point out where in my understanding of these commands I'm going astray!</p>
 

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