Forum: help

RE: cs_lu(A) failed: near-singular A (or out of memory) [ Reply ] By: Douglas Bates on 2012-12-10 15:56	[forum:38632]
The problem is that the system matrix, xtOmegaInv %*% xMat2, is computationally singular. You will need to re-examine the computational method.

cs_lu(A) failed: near-singular A (or out of memory) [ Reply ]
By: Rui Neiva on 2012-12-09 22:23

[forum:38631]

Hi there everyone,

I have the following model (this is naturally a simplified version just for showing my problem, in case you're wondering this is a translog cost function with the associated cost share equations):

C ~ α + β1 log X + β2 log Y + γ1 log Z + γ2 log XX
C1 ~ β1 + β2 log YY + γ1 log ZZ

Then I have some restrictions on the coefficients, namely that the sum of β equal 1 and the some of γ equal zero
So, I've added the following equations to the model

C2 ~ 0 + β1.Y1 + β2.Y2
C3 ~ 0 + γ1.Y3 + γ2. Y4

I've created columns in my data frame with values of 0 for variable C3 and values of 1 for Y1, Y2, Y3, Y4 and C2

I'm using the systemfit package to solve a multiple equation system using the SURE method, and using a matrix to impose the restrictions on the coefficients (i.e., that the β1 in all equations is the same value, and the same for all the other coefficients).

When I try to run the model without the restricting equations (C2, C3) it runs just fine, but when I add these two equations I get the error:

"Error in solve(xtOmegaInv %*% xMat2, xtOmegaInv %*% yVec, tol = solvetol) :
cs_lu(A) failed: near-singular A (or out of memory)"

Any ideas on what the problem might be?