How to find the reverse of a permutation vector?

Dear all,

I have a permutation vector

p = [1 3 2 4];

and I define its corresponding permutation matrix is

P = [1 0 0 0 ; 0 0 1 0 ; 0 1 0 0 ; 0 0 0 1 ]; Then the transpose of P is P' = P.

So what's the corresponding permutation vector of P', said pt?

In this case, pt = p since P' = P.

So, are there any fast way (matlab function) to compute permutation vector pt for a given p, for more general case?

Thanks

Paul

Answer 1

[Jan]

Do you want this:

p = [1 3 2 4];
pt(p) = 1:length(p);

[Po-Yu (Paul) Chen]

Thanks Jan ^^

Answer 2

[Jovana Dzunic]

Try this code

zerop=1:4;
p=[1,3,2,4];
invp(p)=zerop(1:4)

Answer 3

[Hugo]

Notice that

p = P * (1:4)'

The same for pt, i.e.

pt = P' * (1:4)'

For vectors p of length N, just use:

pt= P' * (1:N)'

The transpose in (1:N)' is only there to ensure that (1:N) is a column vector.