The find function determines the indices of array elements that meet a given logical
condition. In its simplest form, find returns a column vector of indices. Transpose that
vector to obtain a row vector of indices. For example,
k = find(isprime(A))'
picks out the locations, using one-dimensional indexing, of the primes in the magic square.
k = 2 5 9 10 11 13
Display those primes, as a row vector in the order determined by k, with
A(k) ans = 5 3 2 11 7 13
When you use k as a left-hand-side index in an assignment statement, the matrix structure
A(k) = NaN A = 16 NaN NaN NaN NaN 10 NaN 8 9 6 NaN 12 4 15 14 1