.. default-domain:: chpl

.. module:: LayoutCS

LayoutCS
========
**Usage**

.. code-block:: chapel

   use LayoutCS;


or

.. code-block:: chapel

   import LayoutCS;
.. class:: CS

   
   This CS layout provides a Compressed Sparse Row (CSR) and Compressed Sparse
   Column (CSC) implementation for Chapel's sparse domains and arrays.
   
   To declare a CS domain, invoke the ``CS`` initializer in a `dmapped` clause,
   specifying CSR vs. CSC format with the ``param compressRows`` argument, which
   defaults to ``true`` if omitted. For example:
   
     .. code-block:: chapel
   
       use LayoutCS;
       var D = {0..#n, 0..#m};  // a default-distributed domain
       var CSR_Domain: sparse subdomain(D) dmapped CS(compressRows=true); // Default argument
       var CSC_Domain : sparse subdomain(D) dmapped CS(compressRows=false);
   
   To declare a CSR or CSC array, use a CSR or CSC domain, respectively.
   For example:
   
     .. code-block:: chapel
   
       // assumes the above declarations
       var CSR_Array: [CSR_Domain] real;
       var CSC_Array: [CSC_Domain] real;
   
   This domain map is a layout, i.e. it maps all indices to the current locale.
   All elements of a CS-distributed array are stored
   on the locale where the array variable is declared.  By default, the CS
   layout stores sparse indices in sorted order.  However, this default can
   be changed for a program by compiling with ``-sLayoutCSDefaultToSorted=false``,
   or for a specific domain by passing ``sortedIndices=false`` as an argument
   to the ``CS()`` initializer.