Sorting complex array with cplxpair and how to get the sort index?

I have a vector of complex numbers, which I sort using cplxpair to get the complex conjugates in ordered pair. But now I need to know the index with respect to the orginal vector.

For example,

I have,

k = [

0.0000 - 0.9998i

0.0000 - 0.9995i

0.0000 + 0.9998i

0.0000 + 0.9995i

-0.0001 - 0.9491i

0.0000 + 0.9995i

0.0000 - 0.9995i

-0.0001 + 0.9491i

]

I use cplxpair(k) and I get,

kp = [

-0.0001 - 0.9491i

-0.0001 + 0.9491i

0.0000 - 0.9998i

0.0000 + 0.9998i

0.0000 - 0.9995i

0.0000 + 0.9995i

0.0000 - 0.9995i

0.0000 + 0.9995i

]

But I need to know how to get the index of 'kp' relating to that of 'k'.

[VBBV]

Use find function

Answer 1

[Paul]

ismember() might be what you're looking for. Do you care about how this works if the elements of k are not all unique?

k = [
   0.0000 - 0.9998*1i
   0.0000 - 0.9995*1i
   0.0000 + 0.9998*1i
   0.0000 + 0.9995*1i
  -0.0001 - 0.9491*1i
   0.0000 + 0.9995*1i
   0.0000 - 0.9995*1i
  -0.0001 + 0.9491*1i];
kp = cplxpair(k);
[~,ind] = ismember(k,kp);
[kp(ind) k]

ans = 
   0.0000 - 0.9998i   0.0000 - 0.9998i
   0.0000 - 0.9995i   0.0000 - 0.9995i
   0.0000 + 0.9998i   0.0000 + 0.9998i
   0.0000 + 0.9995i   0.0000 + 0.9995i
  -0.0001 - 0.9491i  -0.0001 - 0.9491i
   0.0000 + 0.9995i   0.0000 + 0.9995i
   0.0000 - 0.9995i   0.0000 - 0.9995i
  -0.0001 + 0.9491i  -0.0001 + 0.9491i

isequal(kp(ind),k)

ans = logical
   1

Note that k contained duplicate values, so ind is not just a shuffle of 1:8

sort(ind).'

ans = 1×8

1 2 3 4 5 5 6 6

[Murthy MVVS]

Thank you 🙏.