> w [,1] [,2] [,3] [,4] 1:1 0.0 0.5 0.5 0.0 2:1 0.5 0.0 0.0 0.5 1:2 0.5 0.0 0.0 0.5 2:2 0.0 0.5 0.5 0.0 > solve(w) Error in solve.default(w) : Lapack routine dgesv: system is exactly singular what does the error mean?