Running examples in 'psychotools-Ex.R' failed
The error most likely occurred in:

> ### Name: pcmodel
> ### Title: Partial Credit Model Fitting Function
> ### Aliases: pcmodel PCModel.fit print.pcmodel summary.pcmodel
> ###   print.summary.pcmodel coef.pcmodel bread.pcmodel estfun.pcmodel
> ###   logLik.pcmodel vcov.pcmodel
> ### Keywords: regression
> 
> ### ** Examples
> 
> o <- options(digits = 4)
> 
> ## Verbal aggression data
> data("VerbalAggression", package = "psychotools")
> 
> ## Partial credit model for the other-to-blame situations
> pcm <- pcmodel(VerbalAggression$resp[, 1:12])
Warning in log(elementary_symmetric_functions(par = esf_par, order = 0,  :
  NaNs produced
> summary(pcm)

Partial credit model

Item category parameters:
               Estimate Std. Error z value Pr(>|z|)
S1WantCurse-C2   0.3610         NA      NA       NA
S1DoCurse-C1    -0.2668         NA      NA       NA
S1DoCurse-C2     0.5382         NA      NA       NA
S1WantScold-C1   0.4993         NA      NA       NA
S1WantScold-C2   1.1292         NA      NA       NA
S1DoScold-C1     0.5465         NA      NA       NA
S1DoScold-C2     1.6738         NA      NA       NA
S1WantShout-C1   0.7749         NA      NA       NA
S1WantShout-C2   2.3515         NA      NA       NA
S1DoShout-C1     1.6278         NA      NA       NA
S1DoShout-C2     3.5179         NA      NA       NA
S2WantCurse-C1  -0.5001         NA      NA       NA
S2WantCurse-C2  -0.1174         NA      NA       NA
S2DoCurse-C1     0.0772         NA      NA       NA
S2DoCurse-C2     0.8877         NA      NA       NA
S2WantScold-C1   0.2850         NA      NA       NA
S2WantScold-C2   1.0500         NA      NA       NA
S2DoScold-C1     0.9056         NA      NA       NA
S2DoScold-C2     2.4845         NA      NA       NA
S2WantShout-C1   0.9201         NA      NA       NA
S2WantShout-C2   2.1468         NA      NA       NA
S2DoShout-C1     2.0264         NA      NA       NA
S2DoShout-C2     4.1038         NA      NA       NA

Log-likelihood: -2480 (df = 23) 
Number of iterations in BFGS optimization: 10 

> 
> ## visualizations
> plot(pcm, type = "profile")
> plot(pcm, type = "regions")
> plot(pcm, type = "curves")
> plot(pcm, type = "information")
> plot(pcm, type = "piplot")
> 
> ## Get data of situation 1 ('A bus fails to
> ## stop for me') and induce a null category in item 2.
> pcd <- VerbalAggression$resp[, 1:6, drop = FALSE]
> pcd[pcd[, 2] == 1, 2] <- NA
> 
> ## fit pcm to these data, comparing downcoding and keeping strategy
> pcm_va_keep  <- pcmodel(pcd, nullcats = "keep")
Warning in pcmodel(pcd, nullcats = "keep") :
  There are items with null categories (I2).
Warning in log(elementary_symmetric_functions(par = esf_par_i, order = 0,  :
  NaNs produced
Warning in log(elementary_symmetric_functions(par = esf_par_i, order = 0,  :
  NaNs produced
Warning in log(elementary_symmetric_functions(par = esf_par_i, order = 0,  :
  NaNs produced
Error in solve.default(vc) : 
  system is computationally singular: reciprocal condition number = 4.08959e-302
Calls: pcmodel -> solve -> solve.default
Execution halted