Driver function .
public static void main ( String args [ ] ) { Lower_triangular ob = new Lower_triangular ( ) ; int mat [ ] [ ] = { { 1 , 0 , 0 , 0 } , { 1 , 4 , 0 , 0 } , { 4 , 6 , 2 , 0 } , { 0 , 4 , 7 , 6 } } ;