MXNet (.json, .params)

Background & Context

    • Underlying format of the MXNet deep learning framework, used by the Wolfram Language.
    • Translation is performed automatically between the low-level layers used by MXNet and corresponding high-level layers used by the Wolfram Language.
    • The mapping between Wolfram Language layers and MXNet layers is not always invertible.
    • Networks saved as MXNet are stored as two separate file: a .json file specifying the network topology and a .params file specifying the numeric arrays used in the network.

Import & Export

  • Import["file.json","MXNet"] imports the MXNet network saved as a .json file, loading weights from a corresponding .params file if available.
  • The parameter file corresponding to "file.json" is assumed to match the pattern "file*.params" and be located in the same folder.
  • Import["file.params","MXNet"] can also be used to directly import network parameters.
  • Import["file.json",{"MXNet",elem}] and Import["file.params",{"MXNet",elem}] import the specified element elem from the corresponding file.
  • By default, Import["file.json"] is imported as a "JSON" format rather than "MXNet".
  • See the following reference pages for full general information:
  • Import, Exportimport from or export to a file
    CloudImport, CloudExportimport from or export to a cloud object
    ImportString, ExportStringimport from or export to a string
    ImportByteArray, ExportByteArrayimport from or export to a byte array

Import Elements

  • Net Import elements, available when importing the .json file:
  • "InputNames"names of the net inputs
    "LayerAssociation"list of rules for options, properties and settings
    "Net"import the net as a NetGraph or NetChain
    "NodeDataset"dataset of MXNet symbol nodes
    "NodeGraph"graph of nodes of MXNet symbol
    "NodeGraphPlot"plot of nodes of MXNet symbol
    "UninitializedNet"import the net without any parameters
  • Import["file.json","MXNet"] uses the "Net" element by default.
  • Parameter Import elements, available when importing the .params file:
  • "ArrayAssociation"import the parameter arrays as an association
    "ArrayList"import the parameter arrays as a list
    "ArrayNames"the names of the parameter arrays
  • Import["file.params","MXNet"] uses the "ArrayAssociation" element by default.

Options

  • Import option:
  • "ArrayPath"Automaticpath to the MXNet parameter file
  • Export options:
  • "ArrayPath"Automaticpath to save the parameter arrays to
    "SaveArrays"Truewhether to export the net parameter arrays

Examples

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Basic Examples  (1)

Define an initialized NetChain:

Export the net to the MXNet format:

Import the net from the MXNet format:

Import Elements  (11)

InputNames  (1)

Obtain a list of net inputs for a given MXNet net:

LayerAssociation  (1)

Obtain an association of layers for a given MXNet net:

Net  (2)

Import an MXNet net as a NetGraph:

This is equivalent to the following:

If an MXNet net has a parameter file with the same name, it is automatically imported as well:

The "ArrayPath" option can be used to avoid importing the parameter file:

This is equivalent to using the "UninitializedNet" content element:

NodeDataset  (1)

View the nodes of an MXNet symbol:

NodeGraph  (1)

Obtain a graph of the nodes in an MXNet symbol:

Get a list of vertices in the graph:

NodeGraphPlot  (1)

Obtain a plot of the nodes in an MXNet symbol:

UninitializedNet  (1)

"UninitializedNet" avoids importing any net parameters:

ArrayAssociation  (1)

Import the arrays in an MXNet net as an association:

This is equivalent to explicitly specifying the path to the parameter file:

ArrayList  (1)

Import the arrays in an MXNet net as a list:

ArrayNames  (1)

Obtain the names of the arrays in an MXNet net:

This is equivalent to:

Import Options  (1)

"ArrayPath"  (1)

"ArrayPath" allows for an explicit path to a parameter file to be specified:

When it is set to None, no parameters are imported:

This is equivalent to the following:

Possible Issues  (3)

Any NetEncoder or NetDecoder attached to a net is not exported:

The imported net no longer has a NetEncoder:

MXNet model definitions do not preserve information about input and output dimensions. Define a NetChain with the dimensions of "Input" specified:

Export the net to the MXNet format:

The dimensions of the input are no longer known:

The dimensions can be added manually using NetReplacePart:

Recurrent layers that operate on variable-length sequences cannot be exported:

Fixing the sequence length allows for the net to be exported:

Recurrent layers can often not be re-imported:

The reason is that they are not exported to a single MXNet operator, but rather as a computational graph unrolled over the sequence length: