Since the step function only returns one single variable, the first value
returned by scan() is also one single variable. So it should be:
h, _ = theano.scan(step , sequences=[x])
If instead you use
[h], _ = theano.scan(step , sequences=[x])
then it is trying to expand that variable into a list of one element, which
it is not able to do since it does not know its length.
On Wednesday, July 26, 2017 at 8:56:03 AM UTC-4, Sunjeet Jena wrote:
>
>
> Any idea why this code is not working?
>
>
> import theano
> from theano import tensor
> from theano import shared
> from theano import function
> import numpy as np
>
> x=tensor.ivector('x')
>
> def step(u_t):
>
>
> h=u_t*1
>
> return h
>
> [h], _ = theano.scan(step , sequences=[x])
>
> f=function([x],[h])
>
> b=[1,2,3,4,5,6]
> print(f(b))
>
> *Error is: *
>
> Traceback (most recent call last):
> File "Test1.py", line 31, in <module>
> [h], _ = theano.scan(step , sequences=x)
> File "/usr/local/lib/python2.7/dist-packages/theano/tensor/var.py", line
> 596, in __iter__
> for i in xrange(theano.tensor.basic.get_vector_length(self)):
> File "/usr/local/lib/python2.7/dist-packages/theano/tensor/basic.py",
> line 4685, in get_vector_length
> raise ValueError("length not known: %s" % msg)
> ValueError: length not known: for{cpu,scan_fn} [id A] ''
> |Subtensor{int64} [id B] ''
> | |Shape [id C] ''
> | | |Subtensor{int64::} [id D] 'x[0:]'
> | | |x [id E]
> | | |Constant{0} [id F]
> | |Constant{0} [id G]
> |Subtensor{:int64:} [id H] ''
> | |Subtensor{int64::} [id D] 'x[0:]'
> | |ScalarFromTensor [id I] ''
> | |Subtensor{int64} [id B] ''
> |Subtensor{int64} [id B] ''
>
> Inner graphs of the scan ops:
>
> for{cpu,scan_fn} [id A] ''
> >Elemwise{mul,no_inplace} [id J] ''
> > |x[t] [id K] -> [id H]
> > |TensorConstant{1} [id L]
>
>
>
>
>
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