Allow 0 length vectors in data readers

[syclik]

Currently, we don't allow zero length vectors. For example, see the bernoulli.stan model. Want:

N <- 0
y <- c()

[bob-carpenter]

We are definitely going to need this one in order to deal with ode solvers, because some of the vectors might need to be zero length.

I also don't think we initialize them properly even if they're not data.

Hopefully, it's just a matter of calling the constructor for std::vector more carefully.

I also re-assigned it to me.

[syclik]

Thanks, Bob. I can help when I'm not buried. Hopefully I beat you to it.

On Fri, Aug 1, 2014 at 1:02 PM, Bob Carpenter notifications@github.com
wrote:

We are definitely going to need this one in order to deal with ode
solvers, because some of the vectors might need to be zero.

I also don't think we initialize them properly even if they're not data.

Hopefully, it's just a matter of calling the constructor for std::vector
more carefully.

I also re-assigned it to me.

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#683 (comment).

[bob-carpenter]

• zero-size matrices
• zero-size vectors and row vectors
• zero-size arrays

Only really need the zero-size arrays to deal with general ODE functions.

[mbrubake]

I've run into use-cases for zero-size arrays when writing more configurable
models. This is useful beyond just ODE functions.