maxval -- find maximum value, and its index, in a vector
  -1 -- local vector -- random numbers
  -2 -- local vector -- forward ramp
  -3 -- local vector -- reverse ramp
  -4 -- mapped vector, parallel backend -- random numbers
  -5 -- mapped vector, parallel backend -- forward ramp
  -6 -- mapped vector, parallel backend -- reverse ramp
  -7 -- mapped vector,  generic backend -- random numbers
  -8 -- mapped vector,  generic backend -- forward ramp
  -9 -- mapped vector,  generic backend -- reverse ramp