From 89f60f39a226bef5ccd8c52dbd57891c3a4d74c7 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Sun, 27 Oct 2019 20:11:36 +0100
Subject: Add README

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+# boltzgen
+
+…a framework for symbolically generating optimized implementations of the Lattice Boltzmann Method.
+
+At the moment this is a more structured and cleaned up version of the OpenCL kernel generator employed by [symlbm_playground](https://tree.kummerlaender.eu/projects/symlbm_playground/). The goal is to build upon this foundation to provide an easy way to generate efficient code using a high level description of various collision models and boundary conditions. This should allow for easy comparision between various streaming patterns and memory layouts.
+
+## Features
+
+* BGK collision step
+* D2Q9, D3Q7, D3Q19 and D3Q27 lattices with automatic weight inference
+* momenta and bounce back boundary conditions
+* equilibrilization and moment collection utility functions
+* optimization via common subexpression elimination
+* array-of-structures and structure-of-arrays memory layouts
+* AB streaming pattern
+* C++ and OpenCL targets
+* simple CLI frontend
+
+## Usage
+
+The development and execution environment is described using a Nix expression in `shell.nix`.
+
+```
+> nix-shell
+> ./boltzgen.py --help
+usage: boltzgen.py [-h] --lattice LATTICE --layout LAYOUT --precision
+                   PRECISION --geometry GEOMETRY --tau TAU [--disable-cse]
+                   [--functions FUNCTIONS [FUNCTIONS ...]]
+                   [--extras EXTRAS [EXTRAS ...]]
+                   language
+
+Generate LBM kernels in various languages using a symbolic description.
+
+positional arguments:
+  language              Target language (currently either "cl" or "cpp")
+
+optional arguments:
+  -h, --help            show this help message and exit
+  --lattice LATTICE     Lattice type (D2Q9, D3Q7, D3Q19, D3Q27)
+  --layout LAYOUT       Memory layout ("AOS" or "SOA")
+  --precision PRECISION
+                        Floating precision ("single" or "double")
+  --geometry GEOMETRY   Size of the block geometry ("x:y(:z)")
+  --tau TAU             BGK relaxation time
+  --disable-cse         Disable common subexpression elimination
+  --functions FUNCTIONS [FUNCTIONS ...]
+                        Function templates to be generated
+  --extras EXTRAS [EXTRAS ...]
+                        Additional generator parameters
+
+> ./boltzgen.py cpp --lattice D2Q9
+\                   --geometry 128:128
+\                   --layout AOS
+\                   --precision double
+\                   --tau 0.52
+\                   --functions default bounce_back_boundary example
+\                   --extras omp_parallel_for moments_vtk | tee kernel.h
+void collide_and_stream(      double* f_next,
+                        const double* f_prev,
+                        std::size_t gid)
+{
+          double* preshifted_f_next = f_next + gid*9;
+    const double* preshifted_f_prev = f_prev + gid*9;
+
+    const double f_curr_0 = preshifted_f_prev[1161];
+    const double f_curr_1 = preshifted_f_prev[1153];
+    const double f_curr_2 = preshifted_f_prev[1145];
+    const double f_curr_3 = preshifted_f_prev[12];
+    const double f_curr_4 = preshifted_f_prev[4];
+[...]
+```
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