smacof (version 2.1-6)

gravity: Gravity dissimilarities

Description

Computes the dissimilarities using a gravity model based on co-occurrences.

Usage

gravity(X, lambda = 1)

Value

gravdiss

Gravity dissimilarities

weightmat

Weight matrix for subsequent smacof computation

co.occ

Matrix with co-occurences

Arguments

X

numeric matrix

lambda

tuning parameter

Author

Patrick Mair

Details

The first step in this function is to compute the co-occurences. Based on the binarized data matrix \(Y\) we compute \(Y'Y\) which leads to the co-occurence matrix. We then use the gravity model to compute the gravity dissimilarities. In order to give more (or less) structure to the MDS solution, the tuning parameter (which defines a power transformation) can be increased (or decreased). In addition, a weight matrix is created that sets cells with no co-occurences to 0. The corresponding weight matrix for blanking out these cells is established automatically in mds().

References

Mair, P., Rusch, T. & Hornik, K. (2014). The Grand Old Party - A party of values? SpringerPlus, 3(697), https://springerplus.springeropen.com/articles/10.1186/2193-1801-3-697

See Also

mds

Examples

data(GOPdtm)
gravD <- gravity(GOPdtm, lambda = 2)
res <- mds(gravD$gravdiss)  
res$weightmat  ## NA's were blanked out when fitting the model
plot(res)