Find Function

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
is preserved.

A(k) = NaN
A =
    16   NaN   NaN   NaN
   NaN    10   NaN     8
     9     6   NaN    12
     4    15    14     1