Vectorize fma (fused-multiply-add)

[aaronjg]

Summary:

Please provide a short couple sentence summary.
Most of the composed functions have been vectorized, however fused-multiply add and some of the others that take two arguments only take reals.

Current Version:

v2.16.0

[bob-carpenter]

Thanks for putting this in as an issue. I thought we had a general issue to vectorize all the scalar binary functions. But I don't see it, so I'll leave this one here.

If someone wants to take them on one at a time before that, that would also work. pow has been the most requested such function.

[aaronjg]

Just saw a post on discourse about this as well. Is it part of this issue? #202

[bob-carpenter]

Yes, #202 listed all the scalar functions at one point that might be vectorized. fma has three arguments, so there'll be eight instantiations for each vectorized version in terms of autodiff types.

[rok-cesnovar]

fma has since been vectorized. These are the supported signatures:

  fma(real, real, real) => real
  fma(real, real, vector) => vector
  fma(real, vector, real) => vector
  fma(real, vector, vector) => vector
  fma(vector, real, real) => vector
  fma(vector, real, vector) => vector
  fma(vector, vector, real) => vector
  fma(vector, vector, vector) => vector
  fma(real, real, row_vector) => row_vector
  fma(real, row_vector, real) => row_vector
  fma(real, row_vector, row_vector) => row_vector
  fma(row_vector, real, real) => row_vector
  fma(row_vector, real, row_vector) => row_vector
  fma(row_vector, row_vector, real) => row_vector
  fma(row_vector, row_vector, row_vector) => row_vector
  fma(real, real, matrix) => matrix
  fma(real, matrix, real) => matrix
  fma(real, matrix, matrix) => matrix
  fma(matrix, real, real) => matrix
  fma(matrix, real, matrix) => matrix
  fma(matrix, matrix, real) => matrix
  fma(matrix, matrix, matrix) => matrix