reg_poly_2nd=: 4 : 0
q=: +/ *: x. - y +/ . * b=: x. %. y=: y.^/ i.3
cd=: (t=: 100 + er=: 0) * 1-q % +/ *: (]-+/%#) x.
while. er<1e_3
 do. er=: +/ b *(t=:t+1)^i.3
end.
b;cd;t
)