public SMat3 Mul_ata(Mat3 a)
{
SMat3 m = new SMat3();
m.SetSymmetric(a.m00 * a.m00 + a.m10 * a.m10 + a.m20 * a.m20,
a.m00 * a.m01 + a.m10 * a.m11 + a.m20 * a.m21,
a.m00 * a.m02 + a.m10 * a.m12 + a.m20 * a.m22,
a.m01 * a.m01 + a.m11 * a.m11 + a.m21 * a.m21,
a.m01 * a.m02 + a.m11 * a.m12 + a.m21 * a.m22,
a.m02 * a.m02 + a.m12 * a.m12 + a.m22 * a.m22);
return m;
}