chore: import upstream snapshot with attribution

docs/calculus/sums_limits.rst

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+Sums, products, limits and extrapolation
+----------------------------------------
+
+The functions listed here permit approximation of infinite
+sums, products, and other sequence limits.
+Use :func:`mpmath.fsum` and :func:`mpmath.fprod`
+for summation and multiplication of finite sequences.
+
+Summation
+..........................................
+
+:func:`~mpmath.nsum`
+^^^^^^^^^^^^^^^^^^^^^
+.. autofunction:: mpmath.nsum
+
+:func:`~mpmath.sumem`
+^^^^^^^^^^^^^^^^^^^^^
+.. autofunction:: mpmath.sumem
+
+:func:`~mpmath.sumap`
+^^^^^^^^^^^^^^^^^^^^^
+.. autofunction:: mpmath.sumap
+
+Products
+...............................
+
+:func:`~mpmath.nprod`
+^^^^^^^^^^^^^^^^^^^^^^
+.. autofunction:: mpmath.nprod
+
+Limits (``limit``)
+..................
+
+:func:`~mpmath.limit`
+^^^^^^^^^^^^^^^^^^^^^^
+.. autofunction:: mpmath.limit
+
+Extrapolation
+..........................................
+
+The following functions provide a direct interface to
+extrapolation algorithms. :func:`~mpmath.nsum` and :func:`~mpmath.limit`
+essentially work by calling the following functions with an increasing
+number of terms until the extrapolated limit is accurate enough.
+
+The following functions may be useful to call directly if the
+precise number of terms needed to achieve a desired accuracy is
+known in advance, or if one wishes to study the convergence
+properties of the algorithms.
+
+
+:func:`~mpmath.richardson`
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+.. autofunction:: mpmath.richardson
+
+:func:`~mpmath.shanks`
+^^^^^^^^^^^^^^^^^^^^^^^
+.. autofunction:: mpmath.shanks
+
+:func:`~mpmath.levin`
+^^^^^^^^^^^^^^^^^^^^^^
+.. autofunction:: mpmath.levin
+
+:func:`~mpmath.cohen_alt`
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+.. autofunction:: mpmath.cohen_alt
+