public void Rot12(ref float c, ref float s)
{
Mat3.CalcSymmetricGivensCoefficients(m11, m12, m22, out c, out s);
float cc = c * c;
float ss = s * s;
float mix = 2 * c * s * m12;
SetSymmetric(m00, c * m01 - s * m02, s * m01 + c * m02,
cc * m11 - mix + ss * m22, 0, ss * m11 + mix + cc * m22);
}