Hello,
I'm facing a similar error and I don't have significant experience with
scan. When I attempted to solve it with dimshuffle, I get another error
that I don't expect.
Any suggestions?
Many thanks.
On Wednesday, 17 February 2016 16:14:11 UTC+1, Dzmitry Bahdanau wrote:
>
> Hi all,
>
> I have significant experience with theano.scan, but its error messages
> were always incomprehensible for me. Perhaps this is the day to figure out
> how to read them..
>
> Here is a typical error message that I got this morning:
>
>
> * When compiling the inner function of scan (the function called by scan
> in each of its iterations) the following error has been encountered: The
> initial state (`outputs_info` in scan nomenclature) of variable
> IncSubtensor{Set;:int64:}.0 (argument number 0) has 3 dimension(s), while
> the corresponding variable in the result of the inner function of scan
> (`fn`) has 3 dimension(s) (it should be one less than the initial state).
> For example, if the inner function of scan returns a vector of size d and
> scan uses the values of the previous time-step, then the initial state in
> scan should be a matrix of shape (1, d). The first dimension of this matrix
> corresponds to the number of previous time-steps that scan uses in each of
> its iterations. In order to solve this issue if the two varialbe currently
> have the same dimensionality, you can increase the dimensionality of the
> variable in the initial state of scan by using dimshuffle or shape_padleft.
> *
> Now, I know that it means that my "outputs_info" don't match the variable
> returned by inner scan function. But let me try to read this error message
> literally:
>
>
>
> *The initial state (`outputs_info` in scan nomenclature) of variable
> IncSubtensor{Set;:int64:}.0 (argument number 0) has 3 dimension(s), while
> the corresponding variable in the result of the inner function of scan
> (`fn`) has 3 dimension(s)*All right, let's look what we have in
> outputs_info
>
>
>
>
>
> *ipdb> outputs_info[None, Rebroadcast{0}.0]ipdb> outputs_info[1].ndim2*
> Oops! First of all, there is no *IncSubtensor{Set;:int64:}.0, *in this
> list. In addition, there is no variable with 3 dimensions. But let's look
> further:
>
>
>
> *For example, if the inner function of scan returns a vector of size d and
> scan uses the values of the previous time-step, then the initial state in
> scan should be a matrix of shape (1, d). *While I believe that providing
> an initial state of shape (1, d) would probably work, nobody does this,
> including the official scan tutorial! The standard practice in such case is
> to provide a d-vector as an initial state. In the common case when only
> previous state results are used, it is perfectly fine to have the initial
> state and the value returned by scan function with the same shape!
>
> This error message gives me a double blow: first it is incomprehensible,
> second, it postulates that I have always been using Scan in wrong way, and
> makes me wonder, how it ever worked. The only useful information in this
> message is that the result of the inner function has 3 dimensions. This was
> actually helpful in fixing the bug.
>
> I would be curious to hear the opinion of Theano developers, can we
> somehow make this super common error message less confusing?
>
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