Set the upper left 3x3 submatrix of this {@link Matrix4d} to that of the given {@link Matrix4d} and don't change the other elements.
@param mat the {@link Matrix4d} @return this
See Implementation
Set the upper left 3x3 submatrix of this {@link Matrix4d} to that of the given {@link Matrix4d} and don't change the other elements.
@param mat the {@link Matrix4d} @return this