Hi, Tom!
something like this could work:
Sum[If[i > j, cs[i, j], 0], {i, 1, Floor[line]}, {j, 0, Floor[line] - i}]
or:
Sum[cs[i, j], {i, 1, Floor[line]}, {j, 0, Min[Floor[line] - i, i - 1]}]
Both ways work perfect, great thinking man, thank you for your assistance!