Returns candidates for a cell in a sudoku.
C = sudoku_cellcandidates ( X , i , j )
a 9-by-9 matrix, with 0 for unknown entries.
an integer index in the interval 1, 2, ..., 9
an integer index in the interval 1, 2, ..., 9
a row matrix of candidates for the current cell
Returns candidates for the entry (i,j) in a sudoku X.
Programming Sudoku, Wei-Meng Lee, 2006