pm ← {⍵∘.=⍳≢⍵}    ⍝ permutation to matrix
   mp ← ⍳∘1⍤1        ⍝ matrix to permutation

   p                     x
6 3 2 1 5 4 0         96 84 59 5 19 47 36

   pm p      
0 0 0 0 0 0 1            x[p]
0 0 0 1 0 0 0         36 5 59 84 47 19 96
0 0 1 0 0 0 0
0 1 0 0 0 0 0            (pm p)+.×x
0 0 0 0 0 1 0         36 5 59 84 47 19 96
0 0 0 0 1 0 0
1 0 0 0 0 0 0

   mp pm p
6 3 2 1 5 4 0