Matlab array broadcasts like Python

Array broadcasting (no bsxfun() needed) is in Matlab and GNU Octave

Array broadcasting can minimize copying of large arrays in memory or excessive looping over arrays, both of which can be very inefficient. However, there are certain cases particularly with JIT compilers where looping can be faster than array broadcasting. Often the clean, clear code enabled by array broadcasting outweighs those edge-case possible gains. As always, make a simple benchmark if you’re concerned about a particular case (broadcast vs. loop) and for Python try Numba.

bsxfun is no longer needed for:

  • plus
  • minus
  • times
  • rdivide
  • ldivide
  • power

and many more operations.

Example

If A has size 4x5 and B has shape 1x5, A .* B, A + B etc. just work without bsxfun(), provided the N-D array dimension multiplied is of matching shape.

This is important for clarity and conciseness of syntax. bsxfun() is a factor that drove me to using Python over Matlab almost entirely.

Fix errors

A .* B

can result in

error: operator *: nonconformant arguments (op1 is 5x4, op2 is 1x5)

Assuming A and B are compatibly shaped when transposed, try:

A .* B.'

Use .' to transpose because ' means take the Hermetian (complex conjugate) transpose. Remember that Matlab does memory copies (expensive for large arrays) on transpose. Python transposes are “free” O(1) since they’re just a view into the original array (pointer tricks).

Minimum versions

Programs earlier than these versions did require bsxfun().

Programminimum version
MatlabR2016b
Octave3.6.0

Fortran array broadcasting

Fortran 95 brought the spread() function, which allows efficient array broadcasting, at the price of replicating the array in memory.