mvpa2.mappers.svd.ProjectionMapper¶

class mvpa2.mappers.svd.ProjectionMapper(demean=True, **kwargs)¶

Linear mapping between multidimensional spaces.

This class cannot be used directly. Sub-classes have to implement the _train() method, which has to compute the projection matrix _proj and optionally offset vectors _offset_in and _offset_out (if initialized with demean=True, which is default) given a dataset (see _train() docstring for more information).

Once the projection matrix is available, this class provides functionality to perform forward and backwards linear mapping of data, the latter by default using pseudo-inverse (but could be altered in subclasses, like hermitian (conjugate) transpose in case of SVD). Additionally, ProjectionMapper supports optional selection of arbitrary component (i.e. columns of the projection matrix) of the projection.

Forward and back-projection matrices (a.k.a. projection and reconstruction) are available via the proj and recon properties.

Notes

Available conditional attributes:

calling_time+: Time (in seconds) it took to call the node
raw_results: Computed results before invoking postproc. Stored only if postproc is not None.
trained_dataset: The dataset it has been trained on
trained_nsamples+: Number of samples it has been trained on
trained_targets+: Set of unique targets (or any other space) it has been trained on (if present in the dataset trained on)
training_time+: Time (in seconds) it took to train the learner

(Conditional attributes enabled by default suffixed with +)

Attributes

`auto_train`	Whether the Learner performs automatic trainingwhen called untrained.
`descr`	Description of the object if any
`force_train`	Whether the Learner enforces training upon every call.
`is_trained`	Whether the Learner is currently trained.
`pass_attr`	Which attributes of the dataset or self.ca to pass into result dataset upon call
`postproc`	Node to perform post-processing of results
`proj`	Projection matrix
`recon`	Backprojection matrix
`space`	Processing space name of this node

Methods

`__call__`(ds)
`forward`(data)	Map data from input to output space.
`forward1`(data)	Wrapper method to map single samples.
`generate`(ds)	Yield processing results.
`get_postproc`()	Returns the post-processing node or None.
`get_space`()	Query the processing space name of this node.
`reset`()
`reverse`(data)	Reverse-map data from output back into input space.
`reverse1`(data)	Wrapper method to map single samples.
`set_postproc`(node)	Assigns a post-processing node
`set_space`(name)	Set the processing space name of this node.
`train`(ds)	The default implementation calls `_pretrain()`, `_train()`, and finally `_posttrain()`.
`untrain`()	Reverts changes in the state of this node caused by previous training

Initialize the ProjectionMapper

Parameters:

demean : bool

Either data should be demeaned while computing projections and applied back while doing reverse()

enable_ca : None or list of str

Names of the conditional attributes which should be enabled in addition to the default ones

disable_ca : None or list of str

Names of the conditional attributes which should be disabled

auto_train : bool

Flag whether the learner will automatically train itself on the input dataset when called untrained.

force_train : bool

Flag whether the learner will enforce training on the input dataset upon every call.

space : str, optional

Name of the ‘processing space’. The actual meaning of this argument heavily depends on the sub-class implementation. In general, this is a trigger that tells the node to compute and store information about the input data that is “interesting” in the context of the corresponding processing in the output dataset.

pass_attr : str, list of str|tuple, optional

Additional attributes to pass on to an output dataset. Attributes can be taken from all three attribute collections of an input dataset (sa, fa, a – see Dataset.get_attr()), or from the collection of conditional attributes (ca) of a node instance. Corresponding collection name prefixes should be used to identify attributes, e.g. ‘ca.null_prob’ for the conditional attribute ‘null_prob’, or ‘fa.stats’ for the feature attribute stats. In addition to a plain attribute identifier it is possible to use a tuple to trigger more complex operations. The first tuple element is the attribute identifier, as described before. The second element is the name of the target attribute collection (sa, fa, or a). The third element is the axis number of a multidimensional array that shall be swapped with the current first axis. The fourth element is a new name that shall be used for an attribute in the output dataset. Example: (‘ca.null_prob’, ‘fa’, 1, ‘pvalues’) will take the conditional attribute ‘null_prob’ and store it as a feature attribute ‘pvalues’, while swapping the first and second axes. Simplified instructions can be given by leaving out consecutive tuple elements starting from the end.

postproc : Node instance, optional

Node to perform post-processing of results. This node is applied in __call__() to perform a final processing step on the to be result dataset. If None, nothing is done.

descr : str

Description of the instance

Attributes

`auto_train`	Whether the Learner performs automatic trainingwhen called untrained.
`descr`	Description of the object if any
`force_train`	Whether the Learner enforces training upon every call.
`is_trained`	Whether the Learner is currently trained.
`pass_attr`	Which attributes of the dataset or self.ca to pass into result dataset upon call
`postproc`	Node to perform post-processing of results
`proj`	Projection matrix
`recon`	Backprojection matrix
`space`	Processing space name of this node

Methods

`__call__`(ds)
`forward`(data)	Map data from input to output space.
`forward1`(data)	Wrapper method to map single samples.
`generate`(ds)	Yield processing results.
`get_postproc`()	Returns the post-processing node or None.
`get_space`()	Query the processing space name of this node.
`reset`()
`reverse`(data)	Reverse-map data from output back into input space.
`reverse1`(data)	Wrapper method to map single samples.
`set_postproc`(node)	Assigns a post-processing node
`set_space`(name)	Set the processing space name of this node.
`train`(ds)	The default implementation calls `_pretrain()`, `_train()`, and finally `_posttrain()`.
`untrain`()	Reverts changes in the state of this node caused by previous training

proj¶: Projection matrix

recon¶: Backprojection matrix