Dear friends - based on published data I have simulated double exponential decay and tried to recover the known parameters, I get divergensies and bad pairs plots. Did I do something very wrong or is it not possible this way? Below are the simulation and model. All best wishes Troels

library(brms)

Time <- seq(1,60,by=1)

A <- 275; B <- 140; g1 <- 0.1105; g2 <- .0161

Y <- A*exp(-g1*Time) + B*exp(-g2*Time)

Y <- Y + rnorm(60,0,0.5*sqrt(Y))

plot(Time,Y,pch=19,cex=.5)

plot(Time,log(Y),pch=19,cex=.5)

dat1 <- data.frame(Time,Y)

prior1 <- c(prior(normal(275,2),nlpar=“A”),

prior(normal(140,2),nlpar=“B”),

prior(normal(.1,.002),nlpar=“g1”),

prior(normal(01,.005),nlpar=“g2”)

)

fit1 <- brm(bf(Y~A*exp(-g1*Time)+B*exp(-g2*Time),A+B+g1+g2 ~1,nl=TRUE),

data=dat1,cores=4,prior = prior1,chains=4,control = list(adapt_delta = 0.99,max_treedepth = 20),iter = 8000)