When comparing Theano vs CNTK, the Slant community recommends Theano for most people. In the question“What are the best artificial intelligence frameworks?” Theano is ranked 1st while CNTK is ranked 5th. The most important reason people chose Theano is:
Theano is a Python library which is very well adapted for numerical tasks often encountered when dealing with deep learning. What makes it well adapted for those tasks is the fact that it combines several paradigms for numerical computations, namely: matrix operations symbolic variable and function definitions Just-in-time compilation to CPU or GPU machine code
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Pros
Pro Well adapted for numerical tasks
Theano is a Python library which is very well adapted for numerical tasks often encountered when dealing with deep learning.
What makes it well adapted for those tasks is the fact that it combines several paradigms for numerical computations, namely:
matrix operations
symbolic variable and function definitions
Just-in-time compilation to CPU or GPU machine code
Pro Optimized for both CPU and GPU
Since all variables are actually symbolic variables, you need to define a function and fill in the values in order to get a value. For example:
# X, y and w are a matrix and vectors respectively
# E is a scalar that depends on the above variables
# to get the value of E we must define:
Efun = theano.function([X,w,y],
E,allow_input_downcast=True)
While this seems like an unnecessary step, it's actually not. Since Theano now has a representation of the whole expression graph for the Efun function, it can compile and optimize the code so that it can run on both CPU and GPU.
Pro Performance
CNTK easily outperforms Theano, TensorFlow, Torch 7, and Caffe with its support of "multi-machine-multi-GPU" backends. Such a setup can be built using Azure's GPU Lab.
Cons
Con Somewhat low level on its own
Theano is one of the oldest deep learning libraries out there and a lot of other widely used libraries have been built on top of it.
But Theano heavily relies on the mathematical side of deep learning and data discovery, having similar features to NumPy or Matlab. This is why it's usually used with other libraries in order to achieve a higher level of abstraction.