The following text is from Concepts of Physics by Dr. H.C.Verma, from the chapter "Magnetic Properties of Matter", page 281, topic "Magnetic Intensity $H$":
Whenever the end effects of a magnetized material can be neglected, the magnetic intensity due to magnetization is zero. This may be the case with a ring-shaped material or in the middle portion of a long rod. The magnetic intensity in a material is then determined by the external sources only, even if the material is magnetized.
Earlier, I came across the following formula: $$\vec H=\frac{\vec{B}}{\mu_0}-\vec I$$ where, $\vec H$ is the magnetic intensity or magnetizing field intensity, $\vec B$ is the resultant magnetic field (vector sum of applied magnetic field and the magnetic field due to magnetization) and $\vec I$ is the intensity of magnetization (magnetic moment per unit volume).
However, I don't understand why the magnetic intensity due to magnetization is zero when there is no significant end effects as said by the author. I thought resultant magnetic field at a particular point inside a material to be equal to the vector sum of the external magnetic field applied and the magnetic field due to magnetization. But this statement is opposite of what I understood.
It would be helpful if you could explain the above quoted statement. Why is the magnetic intensity in a material determined only by the external sources even if the material is magnetized?