R: Update CRF potentials

crf.update {CRF} | R Documentation

## Update CRF potentials

### Description

Update node and edge potentials of CRF model

### Usage

    crf.update(
      crf,
      node.fea = NULL,
      edge.fea = NULL,
      node.ext = NULL,
      edge.ext = NULL
    )

### Arguments

`crf` | The CRF
`node.fea` | The node features matrix with dimension `(n.nf, n.nodes)`
`edge.fea` | The edge features matrix with dimension `(n.ef, n.edges)`
`node.ext` | The extended information of node features
`edge.ext` | The extended information of edge features

### Details

This function updates `node.pot` and `edge.pot` of CRF model by using the current values of parameters and features.

There are two ways to model the relationship between parameters and features. The first one exploits the special structure of features to reduce the memory usage. However it may not suitable for all circumstances. The other one is more straighforward by explicitly specifying the coefficients of each parameter to calculate the potentials, and may use much more memory. Two approaches can be used together.

The first way uses the objects `node.par` and `edge.par` to define the structure of features and provides the feature information in variables `node.fea` and `edge.fea`. The second way directly provides the feature information in variables `node.ext` and `edge.ext` without any prior assumption on feature structure. `node.ext` is a list and each element has the same structure as `node.pot`. `edge.ext` is a list and each element has the same structure as `edge.pot`.

In detail, the node potential is updated as follows:

node.pot[n,i] = exp( ∑_{f} par[node.par[n,i,f]] * node.fea[f,n] + ∑_{k} par[k] * node.ext[[k]][n,i] )

and the edge potential is updated as follows:

edge.pot[[e]][i,j] = exp( ∑_{f} par[edge.par[[e]][i,j,f]] * edge.fea[f,e] + ∑_{k} par[k] * edge.ext[[k]][[e]][i,j] )

### Value

This function will directly modify the CRF and return the same CRF.

### See Also

`crf.nll`, `train.crf`

[Package CRF version 0.4-3 Index]