Add a note how stacked array is handled in liear algebra

Author: antonwolfy

doc/reference/linalg.rst

@@ -108,3 +108,19 @@ Exceptions
    :nosignatures:
 
    dpnp.linalg.LinAlgError
+
+Linear algebra on several matrices at once
+------------------------------------------
+
+Several of the linear algebra routines listed above are able to compute results
+for several matrices at once, if they are stacked into the same array.
+
+This is indicated in the documentation via input parameter specifications such
+as ``a : (..., M, M) {dpnp.ndarray, usm_ndarray}``. This means that if for
+instance given an input array ``a.shape == (N, M, M)``, it is interpreted as a
+"stack" of N matrices, each of size M-by-M. Similar specification applies to
+return values, for instance the determinant has ``det : (...)`` and will in
+this case return an array of shape ``det(a).shape == (N,)``. This generalizes
+to linear algebra operations on higher-dimensional arrays: the last 1 or 2
+dimensions of a multidimensional array are interpreted as vectors or matrices,
+as appropriate for each operation.