Is there a way to ignore mu-referencing error?

[billdenney]

When building this simulation-only model (https://github.com/nlmixr2/nlmixr2lib/blob/igg_kim_2006/inst/modeldb/endogenous/igg_kim_2006.R), I had to change two of the parameters to natural log so that I could get around the mu referencing error below. Is there a better way to skip the mu-referencing error detection?

igg_kim_2006 <- function() {
  description <- "Immunoglobulin G (IgG) model for nonlinear metabolism in healthy subjects"
  reference <- "Kim J, Hayton WL, Robinson JM, Anderson CL. Kinetics of FcRn-mediated recycling of IgG and albumin in human: pathophysiology and therapeutic implications using a simplified mechanism-based model. Clin Immunol. 2007 Feb;122(2):146-55. doi: 10.1016/j.clim.2006.09.001. Epub 2006 Oct 13. PMID: 17046328; PMCID: PMC2791364."
  # parameters from table 1 in paper
  ini({
    jmax <- log(147); label("Maximal rate of FcRn-mediated recycling (Jmax); i.e., in vivo recycling capacity (mg/d/kg")
    km <- log(21); label("Plasma concentration at which a half Jmax reached (Km); The Michaelis constant (mg/mL)")
    kint <- 0.18; label("Fractional intrinsic catabolic rate (1/day)")
    v1 <- 42; label("Vascular compartment volume (mg/kg)")
    css <- 12.1; label("Steady-state plasma concentration (mg/mL)")
  })
  model({
    # Equation 2
    krmr_0 <- jmax/(v1*(km + css))
    jrmr <- krmr_0 * v1 * css
    # Equation 3
    kcat_0 <- kint - krmr_0
    # Equation 1
    jcat_0 <- kcat_0 * v1 * css
    jpro_0 <- jcat_0
    
    krmr <- jmax/(v1*(km + igg))
    kcat <- kint - krmr
    d/dt(igg) <- jpro_0/v1 - kcat*igg
    igg_0 <- css
    igg(0) <- css
  })
}

nlmixr2est::nlmixr(igg_kim_2006)
#> ℹ parameter labels from comments are typically ignored in non-interactive mode
#> ℹ Need to run with the source intact to parse comments
#> Error: syntax/parsing errors:
#> syntax error: 2+ single population parameters in a single mu-referenced expression: 'jmax', 'km'
#> this could occur when a between subject variability parameter is not initialized with a '~'

^{Created on 2025-10-29 with reprex v2.1.1}

[mattfidler]

No, currently there is no way to skip this.

For simulation it doesn't matter, so perhaps it should be a warning in the future instead of a hard error.