Dear all, The background is that I'm trying to fix this bug in the geometry package: https://r-forge.r-project.org/tracker/index.php?func=detail&aid=1993&group_id=1149&atid=4552
Boiled down, the problem is that there exists at least one matrix X for which det(X) != 0 and for which solve(X) fails giving the error "system is computationally singular: reciprocal condition number = ..." (see appended code & attached file). I don't want my function that calls solve(X) to return an error. I can think of two strategies for dealing with this problem: Strategy 1: Some code like this: if (det(X) < epsilon) { warning("Near singular matrix") return(NULL) } return(solve(X)) The problem is then to find what epsilon should be. Strategy 2: Catch the error thrown by solve(X) like this: f <- function(X) { invX <- tryCatch(solve(X), error=function(e) { warning(e) error.flag <<- TRUE}) if (error.flag) return(NULL) return(invX) } This works OK if called without a surrounding try() ret <- f(matrix(0, 2, 2)) ## Gives warning However, if I encase the call to f() in a try statement, I get an error: ret1 <- try(f(matrix(0, 2, 2))) ## Gives error "Lapack routine dgesv: system is exactly singular" This is undesirable. Advice on how to solve the problem with either strategy would be much appreciated - as indeed would be a completely different solution. All the best, David. * * * Code to throw an error in solve(): > X = as.matrix(read.csv("X.csv")) > det(X) [1] 2.32721e-21 > solve(X) Error in solve.default(X) : system is computationally singular: reciprocal condition number = 1.79977e-16 -- David C Sterratt, Research Fellow http://homepages.inf.ed.ac.uk/sterratt Institute for Adaptive and Neural Computation tel: +44 131 651 1739 School of Informatics, University of Edinburgh fax: +44 131 650 6899 Informatics Forum, 10 Crichton Street, Edinburgh EH8 9AB, Scotland * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * NEW BOOK: Principles of Computational Modelling in Neuroscience Sterratt, Graham, Gillies & Willshaw (CUP, 2011). http://www.compneuroprinciples.org The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.
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