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20.1 Distribution argument and variate constraint issues
When an argument to a built-in distribution certainly does not match that distribution’s specification in the Stan Functions Reference, a warning is thrown. This primarily checks if any distribution argument’s bounds at declaration, compile-time value, or subtype at declaration (e.g. simplex
) is incompatible with the domain of the distribution.
For example, consider the following program.
parameters {
real unb_p;
real<lower=0> pos_p;
}
model {
1 ~ poisson(unb_p);
1 ~ poisson(pos_p);
}
The parameter of poisson
should be strictly positive, but unb_p
is not constrained to be positive.
Pedantic mode produces the following warning.
Warning at 'ex-dist-args.stan', line 6, column 14 to column 19:
A poisson distribution is given parameter unb_p as a rate parameter
(argument 1), but unb_p was not constrained to be strictly positive.