For Loop induced matrix manipulation , Relative index matrix

>> a =[1,2,3,0,0,0,0,8,9,0,11,0,0,14,15];

So i have a big matrix and i want to make another matrix b such that it gives me the relative number index(by this what i mean is it gives me the index of representative number next to the matrix a element ) of matrix a.

i tried a for loop but didnt work to what i wanted...

for eq number 15 present in matrix a is the 8th number present(rest are zeroes) in the whole matrix a

%%%%%%%%%%%%%%% DESIRED OUTPUT %%%%%%%%%%%

[a' b']

ans =

     1     1
     2     2
     3     3
     0     0
     0     0
     0     0
     0     0
     8     4
     9     5
     0     0
    11     6
     0     0
     0     0
    14     7
    15     8

Answer 1

[Walter Roberson]

[tf, b] = ismember(a, a(a ~= 0));
[a' b']

[karan]

Bravo!!!!!!!!!!