Install

pip install pyvista-frd-reader

Wheels are available for Linux, macOS, and Windows. Linux wheels require glibc 2.28 or newer. A source build requires CMake and a C++17 compiler. There is no pure-Python fallback.

Read time steps

Use FRDReader when a file contains more than one result step:

reader = pyvista_frd.FRDReader("transient.frd")
print(reader.time_values)

reader.set_active_time_point(3)
mesh = reader.read()

The reader implements PyVista’s time-reader interface. Result blocks are indexed when the file is opened and parsed when their step is first read.

Read node and element sets

Supply a companion input deck to attach boolean set masks to the result:

mesh = pyvista_frd.read("model.frd", inp_path="model.inp")
body = mesh.extract_cells(mesh.cell_data["ELSET:BODY"])
fixed = mesh.extract_points(mesh.point_data["NSET:FIXED"])

pyvista_frd.read_sets("model.inp") returns the original set IDs without an FRD file. Includes, generated ranges, and references to earlier sets are supported. See Node and element sets for naming, missing-ID behavior, and limitations.

Named surfaces

Extract faces using the companion deck’s *SURFACE definitions, with all nodal results from the active step:

reader = pyvista_frd.FRDReader("model.frd", inp_path="model.inp")
wall = reader.read_surface("WALL")
wall.plot(scalars="STRESS_Mises")
surfaces = reader.read_surfaces()  # named MultiBlock

Solid faces retain quadratic midside nodes. Shell sides, planar edges, expanded beam/shell faces, internal faces, and nodal surfaces are supported. See Named surfaces for face numbering, missing-ID handling, dataset validation, and two runnable galleries with all required result files and companion decks included in the source.

Write and convert files

pyvista_frd.write("result_ascii.frd", mesh)
pyvista_frd.write("result_binary.frd", mesh, binary=True)

# Convert the records without building a PyVista mesh.
pyvista_frd.convert("result_binary.frd", "result_ascii.frd", binary=False)

ASCII output stores six significant digits. Binary output is smaller and retains the stored floating-point values. See Writing FRD for format and round-trip details.

Supported FRD data

The reader supports the two ASCII encodings and the float32 and float64 binary encodings. It reads short and long element records, including fixed-width records whose node IDs have no separating spaces.

Supported element types are HE8, PE6, PE15, TE4, HE20, TE10, TR3, TR6, QU4, QU8, BE2, BE3, PY5, and PY13. PY5 and PY13 are the experimental CalculiX pyramid types C3D5 and C3D13.

For each six-component array whose name contains STRESS or STRAIN, the reader adds:

• <NAME>_Mises: von Mises magnitude

• <NAME>_sgMises: von Mises magnitude signed by the tensor trace

• <NAME>_PS1, _PS2, and _PS3: principal values, largest first

Invalid and unsupported elements produce pyvista.InvalidMeshWarning with the source line number. Points use float64 storage. VTK cell connectivity uses 32-bit storage when it fits, otherwise 64-bit storage.

Relationship to PyVista

PyVista includes a Python FRD reader. This package provides a separate C++ implementation and does not replace pyvista.FRDReader or register itself as the handler for pyvista.read.

The conformance suite compares the two readers file by file and array by array. The current external sweep covers 1,766 files with no undocumented divergences. The principal-value comparison uses a numerical tolerance because the implementations use different eigensolvers. Binary FRD is checked against paired ASCII and binary output from CalculiX because PyVista’s reader supports ASCII only.

See Parity for the corpus, method, results, and limitations. See Divergences for the exact behavioral and numerical differences.

C API

The public header is cpp/include/pvfrd/pvfrd.h. It uses a C ABI and can be called from C, C++, or another language with a foreign-function interface.

cmake -S cpp -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build

#include <pvfrd/pvfrd.h>

pvfrd_file *file = NULL;
if (pvfrd_open("mesh.frd", &file) != PVFRD_OK) { /* handle error */ }

const double *points = pvfrd_points(file);
uint64_t n_points = pvfrd_n_points(file);

pvfrd_close(file);

The shared library has no additional link dependencies. Static linking with GCC or Clang also requires -lstdc++ -lm.

Development

cmake -S cpp -B cpp/build -DPVFRD_BUILD_TESTS=ON
cmake --build cpp/build
./cpp/build/pvfrd_tests

pip install -e .[tests]
pytest

The C++ and Python suites share the fixtures in tests/fixtures. tools/mutate.py applies known parser and writer defects and verifies that the intended tests fail.

Documentation

The documentation includes installation, examples, the Python and C APIs, format notes, and verification results.

Credit

Rafal (@3rav) wrote PyVista’s original FRD reader in pyvista#8255. This package reimplements that behavior and vendors the PyVista reader as its conformance reference. Guido Dhondt and Klaus Wittig created CalculiX and its FRD format. See History and credit.

License

This project is MIT licensed. The vendored fast_float header is available under Apache-2.0, MIT, or BSL terms.