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
Warning in log(elementary_symmetric_functions(par = esf_par, order = 0,  :
  NaNs produced
Warning in log(elementary_symmetric_functions(par = esf_par, order = 0,  :
  NaNs produced
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   0.0189         NA      NA       NA    
S1DoCurse-C1    -0.3095         NA      NA       NA    
S1DoCurse-C2     0.0699         NA      NA       NA    
S1WantScold-C1   0.1376         NA      NA       NA    
S1WantScold-C2   0.3332         NA      NA       NA    
S1DoScold-C1     0.2008         NA      NA       NA    
S1DoScold-C2     0.7689         NA      NA       NA    
S1WantShout-C1   0.3920         NA      NA       NA    
S1WantShout-C2   1.3693         NA      NA       NA    
S1DoShout-C1     1.1913         NA      NA       NA    
S1DoShout-C2     2.5875         NA      NA       NA    
S2WantCurse-C1  -1.0588         NA      NA       NA    
S2WantCurse-C2  -1.0154         NA      NA       NA    
S2DoCurse-C1    -0.1669         NA      NA       NA    
S2DoCurse-C2     0.0160         NA      NA       NA    
S2WantScold-C1  -0.0104         NA      NA       NA    
S2WantScold-C2   0.2075         NA      NA       NA    
S2DoScold-C1     0.5132         NA      NA       NA    
S2DoScold-C2     1.4864         NA      NA       NA    
S2WantShout-C1   0.5203     0.0000     Inf   <2e-16 ***
S2WantShout-C2   1.2012         NA      NA       NA    
S2DoShout-C1     1.7069         NA      NA       NA    
S2DoShout-C2     3.5874         NA      NA       NA    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Log-likelihood: -2220 (df = 23) 
Number of iterations in BFGS optimization: 14 

> 
> ## 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).
> pcm_va_down  <- pcmodel(pcd, nullcats = "downcode")
Warning in pcmodel(pcd, nullcats = "downcode") :
  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 = 7.92754e-279
Calls: pcmodel -> solve -> solve.default
Execution halted