FIND FIND Find Non-zero Elements of An Array

Usage

Returns a vector that contains the indicies of all non-zero elements 
in an array.  The usage is

   y = find(x)

The indices returned are generalized column indices, meaning that if 
the array x is of size [d1,d2,...,dn], and the
element x(i1,i2,...,in) is nonzero, then y
will contain the integer
The second syntax for the find command is

   [r,c] = find(x)

which returns the row and column index of the nonzero entries of x.
The third syntax for the find command also returns the values

   [r,c,v] = find(x).

Note that if the argument is a row vector, then the returned vectors
are also row vectors. This form is particularly useful for converting 
sparse matrices into IJV form.

The find command also supports some additional arguments.  Each of the
above forms can be combined with an integer indicating how many results
to return:

   y = find(x,k)

where k is the maximum number of results to return.  This form will return
the first k results.  You can also specify an optional flag indicating 
whether to take the first or last k values:

   y = find(x,k,'first')
   y = find(x,k,'last')

in the case of the 'last' argument, the last k values are returned.