TensorVariable to Array

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I'm trying to evaluate a theano TensorValue expression:

import pymc3
import numpy as np
with pymc3.Model():
    growth = pymc3.Normal('growth_%s' % 'some_name', 0, 10)

x = np.arange(4)
(x * growth).eval()

but get the error

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/danna/.virtualenvs/lib/python2.7/site-packages/theano/gof/graph.py", line 522, in eval
    self._fn_cache[inputs] = theano.function(inputs, self)
  File "/home/danna/.virtualenvs/lib/python2.7/site-packages/theano/compile/function.py", line 317, in function
    output_keys=output_keys)
  File "/home/danna/.virtualenvs/lib/python2.7/site-packages/theano/compile/pfunc.py", line 486, in pfunc
    output_keys=output_keys)
  File "/home/danna/.virtualenvs/lib/python2.7/site-packages/theano/compile/function_module.py", line 1839, in orig_function
    name=name)
  File "/home/danna/.virtualenvs/lib/python2.7/site-packages/theano/compile/function_module.py", line 1487, in __init__
    accept_inplace)
  File "/home/danna/.virtualenvs/lib/python2.7/site-packages/theano/compile/function_module.py", line 181, in std_fgraph
    update_mapping=update_mapping)
  File "/home/danna/.virtualenvs/lib/python2.7/site-packages/theano/gof/fg.py", line 175, in __init__
    self.__import_r__(output, reason="init")
  File "/home/danna/.virtualenvs/lib/python2.7/site-packages/theano/gof/fg.py", line 346, in __import_r__
    self.__import__(variable.owner, reason=reason)
  File "/home/danna/.virtualenvs/lib/python2.7/site-packages/theano/gof/fg.py", line 391, in __import__
    raise MissingInputError(error_msg, variable=r)
theano.gof.fg.MissingInputError: Input 0 of the graph (indices start from 0), used to compute InplaceDimShuffle{x}(growth_some_name), was not provided and not given a value. Use the Theano flag exception_verbosity='high', for more information on this error.

I tried Can someone please help me see what the theano variables actually output? Thank you! I'm using Python 2.7 and theano 1.0.3

theano pymc3 python-2.7
1 Answers

While PyMC3 distributions are TensorVariable objects, they don't technical have any values to be evaluated outside of sampling. If you want values, you have to at least run sampling on the model:

with pymc3.Model():
    growth = pymc3.Normal('growth', 0, 10)

    trace = pymc3.sample(10)

x = np.arange(4)
x[:, np.newaxis]*trace['growth']

If you want to view node values during sampling, you'd need to use theano.tensor.printing.Print objects. For more info, see the PyMC3 debugging tips.

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