Changed name of is_same struct to mult_wrapper and using arrays rather than vectors.
Changed name of is_same struct to mult_wrapper and using arrays rather than vectors.

stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/stan