2D Wave Equation Solver with MPI

Solves the 2D wave equation on a square domain with zero boundary conditions. Uses implicit time stepping with a Gauss-Seidel iterative solver, parallelized via MPI 2D Cartesian domain decomposition.

Quick Start

# 1. Install MPI (Ubuntu/Debian)
sudo apt install libopenmpi-dev
#    or (Arch)
sudo pacman -S openmpi

# 2. Install the Rust toolchain (once)
#    https://rustup.rs
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

# 3. Build libtensogram_ffi.so + fetch tensogram.h (from crates.io)
make tensogram

# 4. Create the Python venv and install tensogram from PyPI
make py-setup

# 5. Build and run (16 MPI ranks by default)
make run

make alone will also build everything; the separate targets above just make the two one-time installation steps visible.

Build System

The project uses a Makefile with configurable variables:

Variable	Default	Description
NP	16	Number of MPI ranks (must be a perfect square)
VENV	.venv	Python virtualenv directory (auto-used if present)
PYTHON	$(VENV)/bin/python3 or python3	Python interpreter for visualization scripts
SKIP	10	Frame skip for GIF generation
FRAME	150	Frame index for static benchmark plots
FILE	bench_raw.tgm	Input file for viz/viz-save targets
NETCDF	0	Set to 1 to link NetCDF

Make Targets

make                 # Build wave.x (auto-builds tensogram if needed)
make tensogram       # Build libtensogram_ffi.so + copy tensogram.h
make py-setup        # Create .venv and pip install tensogram, numpy, matplotlib, Pillow
make run             # Build + run simulation
make bench           # Full pipeline: run + plots + gifs (sequential)
make plots           # Static benchmark PNGs (comparison + errors)
make gifs            # Animated GIF per codec
make viz             # Interactive visualizer (default: bench_raw.tgm)
make viz-save        # Save visualizer output as GIF
make print-tgm       # Debug: show resolved tensogram paths
make clean           # Remove wave.x
make distclean       # Remove wave.x + outputs + vendor/target + venv

Override any variable: make run NP=4, make gifs SKIP=5, make viz FILE=bench_zstd-3.tgm.

Project Structure

Makefile            Build, run, and visualization targets
waveEq.c            Main solver (MPI topology, Gauss-Seidel, time loop)
config.h            Simulation parameters and output toggles
io_tensogram.h      Tensogram benchmark (included when write_tensogram=1)
io_netcdf.h         NetCDF output (included when write_netcdf=1)
tensogram.h         Tensogram C API header (gitignored, copied by `make tensogram`)
vendor/             Cargo helper that fetches tensogram-ffi from crates.io
  Cargo.toml          (depends on `tensogram-ffi = "*"`)
  src/lib.rs          (intentionally empty)
visualize_tgm.py    Animate a single .tgm file (PIL-optimized GIFs)
plot_bench.py       Benchmark report: comparison PNGs + per-codec GIFs
benchmark.md        Compression benchmark results (auto-generated)

Output Formats

Controlled by flags in config.h. Set to 1 to enable, 0 to disable.

Flag	Default	Output file	Requires
write_posix	0	t_NNNN.txt	nothing
write_netcdf	0	grid.nc	libnetcdf
write_tensogram	1	bench_*.tgm	libtensogram_ffi (from crates.io)

Tensogram (default)

Tensogram is a binary format for N-dimensional tensors with built-in compression, published as:

• tensogram-ffi on crates.io — the C FFI library
• tensogram on PyPI — the Python bindings

The C side is fetched and built via a tiny helper crate in vendor/:

make tensogram

Under the hood this runs cargo build --release on vendor/Cargo.toml (which declares tensogram-ffi = "*"), symlinks the produced cdylib into vendor/target/release/libtensogram_ffi.so, and copies tensogram.h from the Cargo registry cache into the project root. No manual version management, no path environment variables, no local tensogram checkout.

To pin a specific version (e.g. for reproducible benchmarks), edit vendor/Cargo.toml:

[dependencies]
tensogram-ffi = "=0.18.1"

NetCDF

Set write_netcdf to 1 and write_tensogram to 0 in config.h, then:

make NETCDF=1

No optional output

Set both write_netcdf and write_tensogram to 0 in config.h:

mpicc -O3 -march=native waveEq.c -o wave.x -lm

Compression Benchmark

When write_tensogram is enabled, the solver captures simulation frames and benchmarks all 21 compression codecs. Each codec writes a separate bench_<name>.tgm file and results are printed as a Markdown table and saved to benchmark.md.

The codecs tested include:

• Lossless: raw, lz4, zstd (levels 1/3/9), blosc2
• Lossless + shuffle: byte shuffle with zstd, lz4, blosc2
• Lossy quantization: simple_packing at 24/16/12 bits per value, combined with zstd, lz4, or szip
• Floating-point lossy: ZFP (fixed rate, fixed accuracy), SZ3 (absolute and relative error bounds)

See benchmark.md for the full results table.

Visualization

The Python scripts need the tensogram PyPI package plus numpy / matplotlib / Pillow. make py-setup installs all of these into a local .venv/:

make py-setup

Manual equivalent:

python3 -m venv .venv
.venv/bin/pip install tensogram numpy matplotlib Pillow

Single file animation

make viz                              # Interactive window (bench_raw.tgm)
make viz FILE=bench_zstd-3.tgm        # Visualize a specific codec
make viz-save                         # Save as GIF
make viz-save SKIP=5                  # Save with custom frame skip

# Zoom into a sub-region using range decode
.venv/bin/python3 visualize_tgm.py bench_raw.tgm 10 --zoom 100:400,100:400 --save

Benchmark comparison

make plots                            # Static PNGs (codec grid + error heatmaps)
make gifs                             # Animated GIF per codec
make bench                            # Full pipeline: run + plots + gifs

NetCDF

ncview grid.nc

Running the Solver

The number of MPI ranks must be a perfect square (1, 4, 9, 16, ...) and the grid size (528 by default) must be divisible by sqrt(ranks).

make run NP=1                         # single process
make run NP=4                         # 2x2 decomposition
make run NP=16                        # 4x4 decomposition (recommended)

Configuration

All parameters are in config.h.

Simulation

Parameter	Default	Description
dx	0.00594998	Grid spacing (gives 528x528 grid)
dt	0.001	Time step
f_to_go	3.14159 (pi)	Domain size
t_to_go	3.0	Total simulation time
gerr_max	1e-6	Gauss-Seidel convergence tolerance

Output

Parameter	Default	Description
write_posix	0	Enable POSIX text file output
write_netcdf	0	Enable NetCDF output
write_tensogram	1	Enable Tensogram compression benchmark
write_interval	10	Write every Nth solver step (reduces output size)
tgm_bench_steps	0	Max frames to capture (0 = all)

Output size control

The solver runs 3001 steps for t=3.0. write_interval controls how many are captured:

write_interval	Frames	Raw size	Covers
1	3001	6.69 GB	every step
10	301	671 MB	every 10th step
20	151	337 MB	every 20th step