[R] R Error: System is computationally singular

[Nathan Svoboda]

Greetings,

I am trying to fit a zero-inflated Poisson model using zeroinfl() from the
pscl library. I have 5 covariates (4 continuous, 1 categorical); the
categorical variable has 7 levels.  I have had success fitting models that
contain only the continuous covariates; however, when I add the categorical
variable to any of the models (or if I run it by itself) I get the following
error: 

Error in solve.default(as.matrix(fit$hessian)) : 

  system is computationally singular: reciprocal condition number =
3.46934e-20

 The code I am using is:

library(pscl)
f1 <- formula(LOCS ~ as.factor(LCOVER) + D_ROADS + D_WATER + D_EDGE +
D_GRASS)
ZIP1 <- zeroinfl(f1, dist="poisson", link = "logit", data = FAWNS)
 
There is no correlation between my covariates. Also, I tried reducing my
categorical covariate to 3 levels and still receive the same error. Can
anyone suggest why I may be getting this error when I add the categorical
covariate?
 
I appreciate your time and input. Thank you,
 
Nate
 
Nathan Svoboda
Graduate Research Assistant
Carnivore Ecology Lab
Mississippi State University

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