Update tensor doc page to provide more information

Author: vlad-perevezentsev

doc/tensor.rst

@@ -4,15 +4,67 @@ Tensor (``dpnp.tensor``)
 ========================
 
 ``dpnp.tensor`` provides a reference implementation of the
-`Python Array API <https://data-apis.org/array-api/latest/>`_ specification. The implementation
-uses data-parallel algorithms suitable for execution on accelerators, such as GPUs.
+`Python Array API <https://data-apis.org/array-api/latest/>`_ specification.
+The implementation uses data-parallel algorithms suitable for execution on
+accelerators, such as GPUs.
 
-``dpnp.tensor`` is written using C++ and `SYCL <https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html>`_
-and oneAPI extensions implemented in `Intel(R) oneAPI DPC++ compiler <https://www.intel.com/content/www/us/en/developer/tools/oneapi/dpc-compiler.html>`_.
+It also provides the underlying Array API-compliant implementation
+used by ``dpnp``.
+
+``dpnp.tensor`` is written using C++ and
+`SYCL <https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html>`_
+and oneAPI extensions implemented in
+`Intel(R) oneAPI DPC++ compiler <https://www.intel.com/content/www/us/en/developer/tools/oneapi/dpc-compiler.html>`_.
+
+Design and Motivation
+---------------------
+
+The tensor implementation was originally developed as a standalone project and
+later integrated into the `dpctl <https://intelpython.github.io/dpctl/latest/index.html>`_
+library as ``dpctl.tensor``. It has since been migrated into ``dpnp``,
+making ``dpnp`` the primary owner and development location of the tensor implementation.
+
+This change simplifies maintenance, reduces cross-project
+dependencies, and enables independent development and release cycles.
+
+Relationship to ``dpnp.ndarray``
+--------------------------------
+
+:class:`dpnp.ndarray` is a high-level array object built on top of
+``dpnp.tensor.usm_ndarray``, storing array data in Unified Shared Memory
+(USM) allocated on a SYCL device. Most users interact with
+:class:`dpnp.ndarray` directly; ``dpnp.tensor.usm_ndarray`` may appear in error
+messages or type signatures when working with device placement or
+interoperability.
+
+Relationship to ``dpctl``
+-------------------------
+
+The migration of ``dpctl.tensor`` into ``dpnp.tensor`` does not replace
+`dpctl <https://intelpython.github.io/dpctl/latest/index.html>`_ itself.
+``dpctl`` remains responsible for device and queue management
+(:class:`dpctl.SyclDevice`, :class:`dpctl.SyclQueue`) as well as USM memory
+allocation. ``dpnp`` builds on top of these capabilities.
+
+Example
+-------
+
+.. code-block:: python
+
+    import dpnp
+    import dpnp.tensor as dpt
+
+    # Create a tensor array on the default device
+    x = dpt.asarray([1.0, 2.0, 3.0])
+
+    # dpnp.ndarray wraps the underlying usm_ndarray
+    a = dpnp.asarray([1.0, 2.0, 3.0])
+    assert isinstance(a.get_array(), dpt.usm_ndarray)
 
 .. note::
 
-   The documentation for ``dpnp.tensor`` API documentation will be added in a future release.
+   The ``dpnp.tensor`` API documentation will be added in a future release.
 
-   For the complete API reference, see the
+   The current implementation remains compatible with the original
+   ``dpctl.tensor`` API. For the complete API reference, see the
    `dpctl 0.21.1 tensor documentation <https://intelpython.github.io/dpctl/0.21.1/api_reference/dpctl/tensor.html>`_.