mxnet.executor

Symbolic Executor component of MXNet.

Classes

Executor(handle, symbol, ctx, grad_req, …)

Executor is the object providing efficient symbolic graph execution and optimization.

class mxnet.executor.Executor(handle, symbol, ctx, grad_req, group2ctx)

Bases: object

Executor is the object providing efficient symbolic graph execution and optimization.

Examples

Attributes

arg_dict	Get dictionary representation of argument arrrays.
aux_dict	Get dictionary representation of auxiliary states arrays.
grad_dict	Get dictionary representation of gradient arrays.
output_dict	Get dictionary representation of output arrays.

Methods

backward([out_grads, is_train])	Do backward pass to get the gradient of arguments.
copy_params_from(arg_params[, aux_params, …])	Copy parameters from arg_params, aux_params into executor’s internal array.
debug_str()	Get a debug string about internal execution plan.
forward([is_train])	Calculate the outputs specified by the bound symbol.
get_optimized_symbol()	Get an optimized version of the symbol from the executor.
reshape([partial_shaping, allow_up_sizing])	Return a new executor with the same symbol and shared memory, but different input/output shapes.
set_monitor_callback(callback[, monitor_all])	Install callback for monitor.

>>> # typical approach to create an executor is to bind symbol
>>> a = mx.sym.Variable('a')
>>> b = mx.sym.Variable('b')
>>> c = 2 * a + b
>>> texec = c.bind(mx.cpu(), {'a': mx.nd.array([1,2]), 'b':mx.nd.array([2,3])})

property arg_dict

Get dictionary representation of argument arrrays.

Returns

arg_dict – The dictionary that maps the names of arguments to NDArrays.

Return type

dict of str to NDArray

:raises ValueError : if there are duplicated names in the arguments.:

property aux_dict

Get dictionary representation of auxiliary states arrays.

Returns

aux_dict – The dictionary that maps name of auxiliary states to NDArrays.

Return type

dict of str to NDArray

:raises ValueError : if there are duplicated names in the auxiliary states.:

backward(out_grads=None, is_train=True)

Do backward pass to get the gradient of arguments.

Parameters

• out_grads (NDArray or list of NDArray or dict of str to NDArray, optional) – Gradient on the outputs to be propagated back. This parameter is only needed when bind is called on outputs that are not a loss function.

• is_train (bool, default True) – Whether this backward is for training or inference. Note that in rare cases you want to call backward with is_train=False to get gradient during inference.

Examples

>>> # Example for binding on loss function symbol, which gives the loss value of the model.
>>> # Equivalently it gives the head gradient for backward pass.
>>> # In this example the built-in SoftmaxOutput is used as loss function.
>>> # MakeLoss can be used to define customized loss function symbol.
>>> net = mx.sym.Variable('data')
>>> net = mx.sym.FullyConnected(net, name='fc', num_hidden=6)
>>> net = mx.sym.Activation(net, name='relu', act_type="relu")
>>> net = mx.sym.SoftmaxOutput(net, name='softmax')

>>> args =  {'data': mx.nd.ones((1, 4)), 'fc_weight': mx.nd.ones((6, 4)),
>>>          'fc_bias': mx.nd.array((1, 4, 4, 4, 5, 6)), 'softmax_label': mx.nd.ones((1))}
>>> args_grad = {'fc_weight': mx.nd.zeros((6, 4)), 'fc_bias': mx.nd.zeros((6))}
>>> texec = net.bind(ctx=mx.cpu(), args=args, args_grad=args_grad)
>>> out = texec.forward(is_train=True)[0].copy()
>>> print out.asnumpy()
[[ 0.00378404  0.07600445  0.07600445  0.07600445  0.20660152  0.5616011 ]]
>>> texec.backward()
>>> print(texec.grad_arrays[1].asnumpy())
[[ 0.00378404  0.00378404  0.00378404  0.00378404]
 [-0.92399555 -0.92399555 -0.92399555 -0.92399555]
 [ 0.07600445  0.07600445  0.07600445  0.07600445]
 [ 0.07600445  0.07600445  0.07600445  0.07600445]
 [ 0.20660152  0.20660152  0.20660152  0.20660152]
 [ 0.5616011   0.5616011   0.5616011   0.5616011 ]]
>>>
>>> # Example for binding on non-loss function symbol.
>>> # Here the binding symbol is neither built-in loss function
>>> # nor customized loss created by MakeLoss.
>>> # As a result the head gradient is not automatically provided.
>>> a = mx.sym.Variable('a')
>>> b = mx.sym.Variable('b')
>>> # c is not a loss function symbol
>>> c = 2 * a + b
>>> args = {'a': mx.nd.array([1,2]), 'b':mx.nd.array([2,3])}
>>> args_grad = {'a': mx.nd.zeros((2)), 'b': mx.nd.zeros((2))}
>>> texec = c.bind(ctx=mx.cpu(), args=args, args_grad=args_grad)
>>> out = texec.forward(is_train=True)[0].copy()
>>> print(out.asnumpy())
[ 4.  7.]
>>> # out_grads is the head gradient in backward pass.
>>> # Here we define 'c' as loss function.
>>> # Then 'out' is passed as head gradient of backward pass.
>>> texec.backward(out)
>>> print(texec.grad_arrays[0].asnumpy())
[ 8.  14.]
>>> print(texec.grad_arrays[1].asnumpy())
[ 4.  7.]

copy_params_from(arg_params, aux_params=None, allow_extra_params=False)

Copy parameters from arg_params, aux_params into executor’s internal array.

Parameters

• arg_params (dict of str to NDArray) – Parameters, dict of name to NDArray of arguments.

• aux_params (dict of str to NDArray, optional) – Parameters, dict of name to NDArray of auxiliary states.

• allow_extra_params (boolean, optional) – Whether allow extra parameters that are not needed by symbol. If this is True, no error will be thrown when arg_params or aux_params contain extra parameters that is not needed by the executor.

Raises

ValueError – If there is additional parameters in the dict but allow_extra_params=False.

Examples

>>> # set parameters with existing model checkpoint
>>> model_prefix = 'mx_mlp'
>>> sym, arg_params, aux_params = mx.model.load_checkpoint(model_prefix, 0)
>>> texec.copy_params_from(arg_params, aux_params)

debug_str()

Get a debug string about internal execution plan.

Returns

debug_str – Debug string of the executor.

Return type

string

Examples

>>> a = mx.sym.Variable('a')
>>> b = mx.sym.sin(a)
>>> c = 2 * a + b
>>> texec = c.bind(mx.cpu(), {'a': mx.nd.array([1,2]), 'b':mx.nd.array([2,3])})
>>> print(texec.debug_str())
Symbol Outputs:
            output[0]=_plus0(0)
Variable:a
--------------------
Op:_mul_scalar, Name=_mulscalar0
Inputs:
        arg[0]=a(0) version=0
Attrs:
        scalar=2
--------------------
Op:sin, Name=sin0
Inputs:
        arg[0]=a(0) version=0
--------------------
Op:elemwise_add, Name=_plus0
Inputs:
        arg[0]=_mulscalar0(0)
        arg[1]=sin0(0)
Total 0 MB allocated
Total 11 TempSpace resource requested

forward(is_train=False, **kwargs)

Calculate the outputs specified by the bound symbol.

Parameters

• is_train (bool, optional) – Whether this forward is for evaluation purpose. If True, a backward call is expected to follow.

• **kwargs – Additional specification of input arguments.

Examples

>>> # doing forward by specifying data
>>> texec.forward(is_train=True, data=mydata)
>>> # doing forward by not specifying things, but copy to the executor before hand
>>> mydata.copyto(texec.arg_dict['data'])
>>> texec.forward(is_train=True)
>>> # doing forward by specifying data and get outputs
>>> outputs = texec.forward(is_train=True, data=mydata)
>>> print(outputs[0].asnumpy())

get_optimized_symbol()

Get an optimized version of the symbol from the executor.

Returns

symbol – Optimized symbol from the executor.

Return type

Symbol

property grad_dict

Get dictionary representation of gradient arrays.

Returns

grad_dict – The dictionary that maps name of arguments to gradient arrays.

Return type

dict of str to NDArray

property output_dict

Get dictionary representation of output arrays.

Returns

output_dict – The dictionary that maps name of output names to NDArrays.

Return type

dict of str to NDArray

:raises ValueError : if there are duplicated names in the outputs.:

reshape(partial_shaping=False, allow_up_sizing=False, **kwargs)

Return a new executor with the same symbol and shared memory, but different input/output shapes. For runtime reshaping, variable length sequences, etc. The returned executor shares state with the current one, and cannot be used in parallel with it.

Parameters

• partial_shaping (bool) – Whether to allow changing the shape of unspecified arguments.

• allow_up_sizing (bool) – Whether to allow allocating new ndarrays that’s larger than the original.

• kwargs (dict of string to tuple of int) – New shape for arguments.

Returns

exec – A new executor that shares memory with self.

Return type

Executor

Examples

>>> a = mx.sym.Variable('a')
>>> b = mx.sym.Variable('b')
>>> c = 2 * a + b
>>> texec = c.bind(mx.cpu(), {'a': mx.nd.zeros((2, 1)), 'b': mx.nd.ones((2,1))})
>>> new_shape = {'a': (4, 2), 'b': (4, 2)}
>>> texec.reshape(allow_up_sizing=True, **new_shape)

set_monitor_callback(callback, monitor_all=False)

Install callback for monitor.

Parameters

• callback (function) – Takes a string and an NDArrayHandle.

• monitor_all (bool, default False) – If true, monitor both input and output, otherwise monitor output only.

Examples

>>> def mon_callback(*args, **kwargs):
>>>     print("Do your stuff here.")
>>>
>>> texe.set_monitor_callback(mon_callback)

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