chainer.functions.forget¶

chainer.functions.
forget
(func, *xs)[source]¶ Calls a function without storing intermediate results.
On a forward propagation, Chainer normally stores all intermediate results of
VariableNode
s on a computational graph as they are required on backward propagation. Sometimes these results consume too much memory.F.forget
forgets such intermediate results on forward propagation, and still supports backpropagation with recalculation.On a forward propagation,
F.forget
calls a given function with given variables without creating a computational graph. That means, no intermediate results are stored. On a backward propagation,F.forget
calls the given function again to create a computational graph for backpropagation.F.forget
reduces internal memory usage, whereas it requires more calculation time as it calls the function twice.Example
Let
f
be a function defined as:>>> def f(a, b): ... return (a + b) * a
and,
x
andy
beVariable
s:>>> x = chainer.Variable(np.random.uniform(1, 1, 5).astype(np.float32)) >>> y = chainer.Variable(np.random.uniform(1, 1, 5).astype(np.float32))
When
z
is calculated asz = f(x, y)
, its intermediate resultx + y
is stored in memory. Instead, if you callf
withF.forget
:>>> z = F.forget(f, x, y)
intermediate
x + y
is forgotten.Note
F.forget
does not support functions which behave differently in multiple calls with the same inputs, such asF.dropout()
andF.negative_sampling()
.Note
In case input argument variables are of Ndimensional array objects, arguments will automatically be converted to
Variable
s. This conversion takes place to ensure that this function is included in the computational graph to enable backward computations.Note
F.forget
does not support double backpropagation.Note
If you want to use
F.forget
to a link which updates the link’s internal information every time the forward computation is called, please ensure that the information is updated just once in a single iteration. You may use thechainer.config.in_recomputing
flag to check if the forward computation is the first call in an iteration. Please see the implementation ofBatchNormalization
for detail. Parameters
 Returns
A variable
func
returns. If it returns a tuple, the method returns a tuple too. Return type