Re: [theano-dev] Disconnected Input in Gradient of Theano Scan Op

[Razvan Pascanu]

I was not able to reproduce the error. What version of Theano are you using ?

It might very well be that you are using an older version of Theano and this bug had already been fixed (there have been a few fixes to the grad method of Scan for specifically this kind of errors). Try getting the latest version of Theano from github and run the code. It does not raise any errors for me. 

HTH,

Razvan

On Tue, May 7, 2013 at 5:19 PM, Ryan Gabbard <ryan.g...@gmail.com> wrote:

Hello everyone,

How are the consider_constant, disconnected_inputs, etc. applied when computing the gradient of a ScanOp?  I am running into a situation, which is described with code on StackOverflow:

http://stackoverflow.com/questions/16426641/disconnected-input-in-gradient-of-theano-scan-op

where I'm getting a DisconnectedInputError for a T.grad() call internal to Scan (in connection_pattern()).  The error is with respect to a variable which should be considered constant, but when I specify it in consider_constant in the top-level gradient call, it doesn't help. Neither does setting disconnected_inputs to 'warn'.

The specific thing it complains about as disconnected is not the variable itself, but rather variable[t], which is perhaps a clue.

Thanks very much,

Ryan

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[Ryan Gabbard]

Hello Razvan,

I was using 0.6.0rc2dev-94592494... . (from mid-Feb.). Updating to the latest from github fixed the problem.

Thank you!

Ryan