public void SetRow(int i, Vector4_d v)
{
this[i, 0] = v.x;
this[i, 1] = v.y;
this[i, 2] = v.z;
this[i, 3] = v.w;
}
public void SetColumn(int i, Vector4_d v)
{
this[0, i] = v.x;
this[1, i] = v.y;
this[2, i] = v.z;
this[3, i] = v.w;
}