What is this code doing and what is it's method that is being used?What does the variable glob represent graphically?

function main t1=-3; 12-3.5; n=16: dt = (12-t]) (2*n); 12 = 0; 13 = 0; *1 = f(t1) - f(t2); for j=2:2:2*n-1 12 - k2 - f( t1-j#dt ); end for j=3:2:2*n-1 13 =13 - f(t1-j *dt ); end glob = (dt/3)*( k1 - 4 12 - 2*k3 ); end function OUT = f( IN ) OUT = IN* IN - 6: end