R/algorithms-pe-nmf.R

Defines functions nmf_update.penmf penmf.objective

#' @include registry-algorithms.R
NULL

###% NMF Algorithm: Pattern Expression NMF
###%
###% Implements the PE-NMF algorithm from Zhang et al (2008).
###%
###% It is implemented using the iterative schema defined by the 
###% NMFStrategyIterative class.
###% The algorithm minimizes the Frobenius norm, with two regularization terms
###% (one for each matrix factor) parametrized by two parameters:
###% 
###% min_{W,H} 1/2 ||V - WH||^2
###% 			+ alpha \sum_{i<>j} W_i^T W_j 
###% 			+ beta \sum_{i,j} H_{ij}
###% 
###% So there is two parameters: alpha and beta.
###% The updates for the matrix factors are (in R notations):
###% 
###% H_{i+1} = H_i ( W_i^T %*% V ) / ( W_i^T %*% W_i %*% H_i + beta)
###% W_{i+1} = W_i ( V %*% H_i^T ) / ( W_i %*% H_i %*% H_i^T + alpha W_i %*% M )
###%
###% with matrix M is full of one with diagonal zero.
###% 
###% @author Renaud Gaujoux
###% @creation 17 Jan 2010
###% 

penmf.objective <- function(fit, x, alpha, beta, ...)
{
	w <- .basis(fit)
	1/2 * sum( (x - fitted(fit))^2 )
		+ alpha * ( crossprod(w) - sum(w^2) )
		+ beta * sum(.coef(fit))
}

nmf_update.penmf <- function(i, x, data, alpha, beta, ...){
	
	# retrieve each factor
	w <- .basis(data); h <- .coef(data);
	
	# At the first iteration initialise matrix M
	if( TRUE || i == 1 ){
		r <- ncol(w)
		M <- matrix(1, nrow=r, ncol=r) - diag(1, r)
		#staticVar('M', M, init=TRUE)
	}
	#else M <- staticVar('M')
	
	#precision threshold for numerical stability
	eps <- 10^-9
	
	# H_{i+1} = H_i ( W_i^T %*% V ) / ( W_i^T %*% W_i %*% H_i + beta)
	h <- h * crossprod(w, x) / ( crossprod(w) %*% h + beta)
	
	# W_{i+1} = W_i ( V %*% H_i^T ) / ( W_i %*% H_i %*% H_i^T + alpha W_i %*% M )
	w <- w * tcrossprod(x, h) / ( w %*% tcrossprod(h) + alpha * w %*% M )
	
	#return the modified data
	.basis(data) <- w; .coef(data) <- h;
	data
}

# register PE-NMF
nmfAlgorithm.peNMF <- setNMFMethod('pe-nmf', objective = penmf.objective
		, model='NMFstd'
		, Update= nmf_update.penmf
		, Stop='stationary')

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NMF documentation built on Aug. 1, 2020, 9:06 a.m.