Initialisations of vectors and arrays

[John Reid]

Hi,

Can I assume vectors, arrays, matrices, etc... are initialised to 0 or are their values undefined at initialisation?

Thanks,
John.

[Michael Betancourt]

Assume that they are undefined and should be explicitly initialized to values 

(rep_vector and rep_matrix come in handy here).

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[Daniel Lee]

+1 for Michael's response. That's the best way to deal with it.

In Stan, real variables declared in transformed data, transformed parameters, and local variables are initialized to NaN, not a number. See http://en.m.wikipedia.org/wiki/NaN. Since real variables in Stan are implemented using double and Stan's automatic differentiation types, which use doubles, these can be set as NaN.

int variables are initialized to 0, I believe. The C++ int type can't represent NaN.

Daniel