...

Note that:

• This loop is interchangeable: the top-to-bottom, left-to-right execution order is also valid since all dependence constraints (as shown by the arrows) are still satisfied.
• The inner loop is not vectorisable since there is a dependence chain linking successive iterations.
  • (to use a vector instruction, need to be able to operate on each element of the vector in parallel)
• Similarly, the outer loop is not parallel
• Interchanging the loop does not improve vectorisability or parallelisability