Adding the element of row 1 to both the elements of row 2 to reduce a step from the loop
if ( $ n > 1 ) $ tri [ 1 ] [ 1 ] = $ tri [ 1 ] [ 1 ] + $ tri [ 0 ] [ 0 ] ; $ tri [ 1 ] [ 0 ] = $ tri [ 1 ] [ 0 ] + $ tri [ 0 ] [ 0 ] ;