ndarray.rst

The N-dimensional array (:class:`ndarray <cupy.ndarray>`)
=========================================================

:class:`cupy.ndarray` is the CuPy counterpart of NumPy :class:`numpy.ndarray`.
It provides an intuitive interface for a fixed-size multidimensional array which resides
in a CUDA device.

For the basic concept of ``ndarray``\s, please refer to the `NumPy documentation <https://numpy.org/doc/stable/reference/arrays.ndarray.html>`_.


.. TODO(kmaehashi): use currentmodule:: cupy
.. autosummary::
   :toctree: generated/

   cupy.ndarray


Conversion to/from NumPy arrays
-------------------------------

:class:`cupy.ndarray` and :class:`numpy.ndarray` are not implicitly convertible to each other.
That means, NumPy functions cannot take :class:`cupy.ndarray`\s as inputs, and vice versa.

- To convert :class:`numpy.ndarray` to :class:`cupy.ndarray`, use :func:`cupy.array` or :func:`cupy.asarray`.
- To convert :class:`cupy.ndarray` to :class:`numpy.ndarray`, use :func:`cupy.asnumpy` or :meth:`cupy.ndarray.get`.

Note that converting between :class:`cupy.ndarray` and :class:`numpy.ndarray` incurs data transfer between
the host (CPU) device and the GPU device, which is costly in terms of performance.


.. TODO(kmaehashi): use currentmodule:: cupy
.. autosummary::
   :toctree: generated/

   cupy.array
   cupy.asarray
   cupy.asnumpy


Code compatibility features
---------------------------

:class:`cupy.ndarray` is designed to be interchangeable with :class:`numpy.ndarray` in terms of code compatibility as much as possible.
But occasionally, you will need to know whether the arrays you're handling are :class:`cupy.ndarray` or :class:`numpy.ndarray`.
One example is when invoking module-level functions such as :func:`cupy.sum` or :func:`numpy.sum`.
In such situations, :func:`cupy.get_array_module` can be used.

.. autosummary::
   :toctree: generated/

   cupy.get_array_module

.. autosummary::
   :toctree: generated/

   cupyx.scipy.get_array_module