exec('rot');
if k <> l, e(k-1) = f
f = cs*s(k) + sn*e(k)
e(k) = cs*e(k) - sn*s(k)
g = sn*s(k+1)
s(k+1) = cs*s(k+1)
exec('rot');
s(k) = f
f = cs*e(k) + sn*s(k+1)
s(k+1) = -sn*e(k) + cs*s(k+1)
g = sn*e(k+1)
e(k+1) = cs*e(k+1)
