Some general Remarks¶

Theano offers quite a bit of flexibility, but has some limitations too. How should you write your algorithm to make the most of what Theano can do?

Limitations¶

Conditional control flow is possible but currently not efficient. The current implementation will evaluate both sides of an if construct (see tensor.switch()).
While- or for-Loops within an expression graph are not supported, but soon will be. A scan op is in theano.sandbox, but not quite ready for mainstream yet.
Neither goto nor recursion is supported or planned within expression graphs.

Remember that your code builds a graph that theano compiles, and you cannot literally put loops into that graph.
Remember that Variables are symbolic of computations, not storage. It does not make sense to reassign to a Variable.