docs: added operators and zfp section

docs/user_guide/source/index.rst

@@ -27,6 +27,7 @@ Funded by the `Exascale Computing Project (ECP) <https://www.exascaleproject.org
    components/components
    engines/virtual_engines
    engines/engines
+   operators/operators
    api_full/api_full
    api_high/api_high
 

docs/user_guide/source/operators/ZFPCompressor.rst

@@ -0,0 +1,56 @@
+*************
+ZFPCompressor
+*************
+
+The ``ZFPCompressor`` Operator is compressor that uses a lossy but optionally
+error-bounded compression to achieve high compression ratios.
+
+ZFP provides compressed-array classes that support high throughput read and
+write random access to individual array elements. ZFP also supports serial and
+parallel (OpenMP and CUDA) compression of whole arrays, e.g., for applications
+that read and write large data sets to and from disk.
+
+ADIOS2 provides a ``ZFPCompressor`` operator that lets you compress an
+decompress variables. Below there is an example of how to invoke
+``ZFPCompressor`` operator:
+
+.. code-block:: c++
+
+    adios2::IO io = adios.DeclareIO("Output");
+    auto ZFPOp    = adios.DefineOperator("ZFPCompressor", adios2::ops::LossyZFP);
+
+    auto var_r32 = io.DefineVariable<float>("r32", shape, start, count);
+    var_r32.AddOperation(ZFPOp, {{adios2::ops::zfp::key::rate, rate}});
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ZFPCompressor Specific parameters
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``ZFPCompressor`` operator accepts the following operator specific
+parameters:
+
++-------------------+---------------------------------------------+
+| ``ZFPCompressor`` available parameters                          |
++===================+=============================================+
+| ``accuracy``      | Fixed absolute error tolerance              |
++-------------------+---------------------------------------------+
+| ``rate``          | Fixed number of bits in a compression unit  |
++-------------------+---------------------------------------------+
+| ``precision``     | Fixed number of uncompressed bits per value |
++-------------------+---------------------------------------------+
+| ``backend``       | Backend device: ``cuda`` ``omp`` ``serial`` |
++-------------------+---------------------------------------------+
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ZFPCompressor Execution Policy
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``ZFPCompressor`` can run in multiple backend devices: GPUs (CUDA), OpenMP, and
+in the host CPU. By default ``ZFPCompressor`` will choose its backend following
+the above order upon the availability of the device adapter.
+
+Exceptionally, if its corresponding ADIOS2 variable contains a CUDA memory
+address, this is a CUDA buffer, the CUDA backend will be called if available.
+
+In any case, the user can manually set the backend using the ZFPOperator
+specific parameter ``backend``.

docs/user_guide/source/operators/operators.rst

@@ -0,0 +1,27 @@
+###################
+Supported Operators
+###################
+
+The Operator abstraction allows ADIOS2 to act upon the user application data,
+either from a ``adios2::Variable`` or a set of Variables in an ``adios2::IO``
+object.  Current supported operations are:
+
+1. Data compression/decompression, lossy and lossless.
+2. Callback functions (C++11 bindings only) supported by specific engines
+
+This section provides a description of the :ref:`Available Operators` in ADIOS2
+and their specific parameters to allow extra-control from the user. Parameters
+are passed in key-value pairs for:
+
+1. Operator general supported parameters.
+
+2. Operator specific supported parameters.
+
+Parameters are passed at:
+
+1. Compile time: using the second parameter of the method
+   ``ADIOS2::DefineOperator``
+
+2. :ref:`Runtime Configuration Files` in the :ref:`ADIOS` component.
+
+.. include:: ZFPCompressor.rst