scan_utils.py 文件源码

def forced_replace(out, x, y):
    """
    Check all internal values of the graph that compute the variable ``out``
    for occurrences of values identical with ``x``. If such occurrences are
    encountered then they are replaced with variable ``y``.

    Parameters
    ----------
    out : Theano Variable
    x : Theano Variable
    y : Theano Variable

    Examples
    --------
    out := sigmoid(wu)*(1-sigmoid(wu))
    x := sigmoid(wu)
    forced_replace(out, x, y) := y*(1-y)

    """
    if out is None:
        return None

    # ``visited`` is a set of nodes that are already known and don't need to be
    # checked again, speeding up the traversal of multiply-connected graphs.
    visited = set()
    def local_traverse(graph, x):
        if graph in visited:
            return []
        visited.add(graph)
        if equal_computations([graph], [x]):
            return [graph]
        elif not graph.owner:
            return []
        else:
            rval = []
            for inp in graph.owner.inputs:
                rval += local_traverse(inp, x)
            return rval
    to_replace = local_traverse(out, x)
    return clone(out, replace=OrderedDict((v, y) for v in to_replace))