# Changes/Release Notes¶

On this page we provide a summary of the main API changes, new features and examples for each release of libCEED.

## Current main branch¶

### New features¶

• CeedScalar can now be set as float or double at compile time.

### Maintainability¶

• Refactored preconditioner support internally to facilitate future development and improve GPU completeness/test coverage.

## v0.9 (Jul 6, 2021)¶

### Interface changes¶

• Minor modification in error handling macro to silence pedantic warnings when compiling with Clang, but no functional impact.

### New features¶

• Add CeedVectorAXPY() and CeedVectorPointwiseMult() as a convenience for stand-alone testing and internal use.

• Add CEED_QFUNCTION_HELPER macro to properly annotate QFunction helper functions for code generation backends.

• Add CeedPragmaOptimizeOff macro for code that is sensitive to floating point errors from fast math optimizations.

• Rust support: split libceed-sys crate out of libceed and publish both on crates.io.

### Examples¶

• Solid mechanics mini-app updated to explore the performance impacts of various formulations in the initial and current configurations.

• Fluid mechanics example adds GPU support and improves modularity.

### Deprecated backends¶

• The /cpu/self/tmpl and /cpu/self/tmpl/sub backends have been removed. These backends were intially added to test the backend inheritance mechanism, but this mechanism is now widely used and tested in multiple backends.

## v0.8 (Mar 31, 2021)¶

### Interface changes¶

• Error handling improved to include enumerated error codes for C interface return values.

• Installed headers that will follow semantic versioning were moved to include/ceed directory. These headers have been renamed from ceed-*.h to ceed/*.h. Placeholder headers with the old naming schema are currently provided, but these headers will be removed in the libCEED v0.9 release.

### Performance improvements¶

• New HIP MAGMA backends for hipMAGMA library users: /gpu/hip/magma and /gpu/hip/magma/det.

• New HIP backends for improved tensor basis performance: /gpu/hip/shared and /gpu/hip/gen.

### Examples¶

• example updated with traction boundary conditions and improved Dirichlet boundary conditions.

• example updated with Neo-Hookean hyperelasticity in current configuration as well as improved Neo-Hookean hyperelasticity exploring storage vs computation tradeoffs.

• example updated with isentropic traveling vortex test case, an analytical solution to the Euler equations that is useful for testing boundary conditions, discretization stability, and order of accuracy.

• example updated with support for performing convergence study and plotting order of convergence by polynomial degree.

## v0.7 (Sep 29, 2020)¶

### New features¶

• New HIP backend: /gpu/hip/ref.

• CeedQFunction support for user CUfunctions in some backends

### Performance improvements¶

• OCCA backend rebuilt to facilitate future performance enhancements.

• Petsc BPs suite improved to reduce noise due to multiple calls to mpiexec.

### Deprecated backends¶

• The /gpu/cuda/reg backend has been removed, with its core features moved into /gpu/cuda/ref and /gpu/cuda/shared.

## v0.6 (Mar 29, 2020)¶

libCEED v0.6 contains numerous new features and examples, as well as expanded documentation in this new website.

### New features¶

• New Python interface using CFFI provides a nearly 1-1 correspondence with the C interface, plus some convenience features. For instance, data stored in the CeedVector structure are available without copy as numpy.ndarray. Short tutorials are provided in Binder.

• Linear QFunctions can be assembled as block-diagonal matrices (per quadrature point, CeedOperatorAssembleLinearQFunction()) or to evaluate the diagonal (CeedOperatorAssembleLinearDiagonal()). These operations are useful for preconditioning ingredients and are used in the libCEED’s multigrid examples.

• The inverse of separable operators can be obtained using CeedOperatorCreateFDMElementInverse() and applied with CeedOperatorApply(). This is a useful preconditioning ingredient, especially for Laplacians and related operators.

• Make public accessors for various attributes to facilitate writing composable code.

• New backend: /cpu/self/memcheck/serial.

• QFunctions using variable-length array (VLA) pointer constructs can be used with CUDA backends. (Single source is coming soon for OCCA backends.)

• Fix some missing edge cases in CUDA backend.

### Examples¶

libCEED-0.6 contains greatly expanded examples with . Notable additions include:

• Standalone (examples/ceed/ex2-surface): compute the area of a domain in 1, 2, and 3 dimensions by applying a Laplacian.

• PETSc (examples/petsc/area.c): computes surface area of domains (like the cube and sphere) by direct integration on a surface mesh; demonstrates geometric dimension different from topological dimension.

• examples/petsc/bpsraw.c (formerly bps.c): transparent CUDA support.

• examples/petsc/bps.c (formerly bpsdmplex.c): performance improvements and transparent CUDA support.

• (examples/petsc/bpssphere.c): generalizations of all CEED BPs to the surface of the sphere; demonstrates geometric dimension different from topological dimension.

• (examples/petsc/multigrid.c): new p-multigrid solver with algebraic multigrid coarse solve.

• (examples/fluids/navierstokes.c; formerly examples/navier-stokes): unstructured grid support (using PETSc’s DMPlex), implicit time integration, SU/SUPG stabilization, free-slip boundary conditions, and quasi-2D computational domain support.

• (examples/solids/elasticity.c): new solver for linear elasticity, small-strain hyperelasticity, and globalized finite-strain hyperelasticity using p-multigrid with algebraic multigrid coarse solve.

## v0.5 (Sep 18, 2019)¶

For this release, several improvements were made. Two new CUDA backends were added to the family of backends, of which, the new cuda-gen backend achieves state-of-the-art performance using single-source . From this release, users can define Q-Functions in a single source code independently of the targeted backend with the aid of a new macro CEED QFUNCTION to support JIT (Just-In-Time) and CPU compilation of the user provided code. To allow a unified declaration, the API has undergone a slight change: the QFunctionField parameter ncomp has been changed to size. This change requires setting the previous value of ncomp to ncomp*dim when adding a QFunctionField with eval mode CEED EVAL GRAD.

Additionally, new CPU backends were included in this release, such as the /cpu/self/opt/* backends (which are written in pure C and use partial E-vectors to improve performance) and the /cpu/self/ref/memcheck backend (which relies upon the Valgrind Memcheck tool to help verify that user have no undefined values). This release also included various performance improvements, bug fixes, new examples, and improved tests. Among these improvements, vectorized instructions for code compiled for CPU were enhanced by using CeedPragmaSIMD instead of CeedPragmaOMP, implementation of a gallery and identity Q-Functions were introduced, and the PETSc benchmark problems were expanded to include unstructured meshes handling were. For this expansion, the prior version of the PETSc BPs, which only included data associated with structured geometries, were renamed bpsraw, and the new version of the BPs, which can handle data associated with any unstructured geometry, were called bps. Additionally, other benchmark problems, namely BP2 and BP4 (the vector-valued versions of BP1 and BP3, respectively), and BP5 and BP6 (the collocated versions—for which the quadrature points are the same as the Gauss Lobatto nodes—of BP3 and BP4 respectively) were added to the PETSc examples. Furthermoew, another standalone libCEED example, called ex2, which computes the surface area of a given mesh was added to this release.

Backends available in this release:

CEED resource (-ceed)

Backend

/cpu/self/ref/serial

Serial reference implementation

/cpu/self/ref/blocked

Blocked reference implementation

/cpu/self/ref/memcheck

Memcheck backend, undefined value checks

/cpu/self/opt/serial

Serial optimized C implementation

/cpu/self/opt/blocked

Blocked optimized C implementation

/cpu/self/avx/serial

Serial AVX implementation

/cpu/self/avx/blocked

Blocked AVX implementation

/cpu/self/xsmm/serial

Serial LIBXSMM implementation

/cpu/self/xsmm/blocked

Blocked LIBXSMM implementation

/cpu/occa

Serial OCCA kernels

/gpu/occa

CUDA OCCA kernels

/omp/occa

OpenMP OCCA kernels

/ocl/occa

OpenCL OCCA kernels

/gpu/cuda/ref

Reference pure CUDA kernels

/gpu/cuda/reg

Pure CUDA kernels using one thread per element

/gpu/cuda/shared

Optimized pure CUDA kernels using shared memory

/gpu/cuda/gen

Optimized pure CUDA kernels using code generation

/gpu/magma

CUDA MAGMA kernels

Examples available in this release:

User code

Example

ceed

• ex1 (volume)

• ex2 (surface)

mfem

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

petsc

• BP1 (scalar mass operator)

• BP2 (vector mass operator)

• BP3 (scalar Laplace operator)

• BP4 (vector Laplace operator)

• BP5 (collocated scalar Laplace operator)

• BP6 (collocated vector Laplace operator)

• Navier-Stokes

nek5000

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

## v0.4 (Apr 1, 2019)¶

libCEED v0.4 was made again publicly available in the second full CEED software distribution, release CEED 2.0. This release contained notable features, such as four new CPU backends, two new GPU backends, CPU backend optimizations, initial support for operator composition, performance benchmarking, and a Navier-Stokes demo. The new CPU backends in this release came in two families. The /cpu/self/*/serial backends process one element at a time and are intended for meshes with a smaller number of high order elements. The /cpu/self/*/blocked backends process blocked batches of eight interlaced elements and are intended for meshes with higher numbers of elements. The /cpu/self/avx/* backends rely upon AVX instructions to provide vectorized CPU performance. The /cpu/self/xsmm/* backends rely upon the LIBXSMM package to provide vectorized CPU performance. The /gpu/cuda/* backends provide GPU performance strictly using CUDA. The /gpu/cuda/ref backend is a reference CUDA backend, providing reasonable performance for most problem configurations. The /gpu/cuda/reg backend uses a simple parallelization approach, where each thread treats a finite element. Using just in time compilation, provided by nvrtc (NVidia Runtime Compiler), and runtime parameters, this backend unroll loops and map memory address to registers. The /gpu/cuda/reg backend achieve good peak performance for 1D, 2D, and low order 3D problems, but performance deteriorates very quickly when threads run out of registers.

A new explicit time-stepping Navier-Stokes solver was added to the family of libCEED examples in the examples/petsc directory (see ). This example solves the time-dependent Navier-Stokes equations of compressible gas dynamics in a static Eulerian three-dimensional frame, using structured high-order finite/spectral element spatial discretizations and explicit high-order time-stepping (available in PETSc). Moreover, the Navier-Stokes example was developed using PETSc, so that the pointwise physics (defined at quadrature points) is separated from the parallelization and meshing concerns.

Backends available in this release:

CEED resource (-ceed)

Backend

/cpu/self/ref/serial

Serial reference implementation

/cpu/self/ref/blocked

Blocked reference implementation

/cpu/self/tmpl

Backend template, defaults to /cpu/self/blocked

/cpu/self/avx/serial

Serial AVX implementation

/cpu/self/avx/blocked

Blocked AVX implementation

/cpu/self/xsmm/serial

Serial LIBXSMM implementation

/cpu/self/xsmm/blocked

Blocked LIBXSMM implementation

/cpu/occa

Serial OCCA kernels

/gpu/occa

CUDA OCCA kernels

/omp/occa

OpenMP OCCA kernels

/ocl/occa

OpenCL OCCA kernels

/gpu/cuda/ref

Reference pure CUDA kernels

/gpu/cuda/reg

Pure CUDA kernels using one thread per element

/gpu/magma

CUDA MAGMA kernels

Examples available in this release:

User code

Example

ceed

• ex1 (volume)

mfem

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

petsc

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

• Navier-Stokes

nek5000

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

## v0.3 (Sep 30, 2018)¶

Notable features in this release include active/passive field interface, support for non-tensor bases, backend optimization, and improved Fortran interface. This release also focused on providing improved continuous integration, and many new tests with code coverage reports of about 90%. This release also provided a significant change to the public interface: a can take any number of named input and output arguments while connects them to the actual data, which may be supplied explicitly to CeedOperatorApply() (active) or separately via CeedOperatorSetField() (passive). This interface change enables reusable libraries of CeedQFunctions and composition of block solvers constructed using . A concept of blocked restriction was added to this release and used in an optimized CPU backend. Although this is typically not visible to the user, it enables effective use of arbitrary-length SIMD while maintaining cache locality. This CPU backend also implements an algebraic factorization of tensor product gradients to perform fewer operations than standard application of interpolation and differentiation from nodes to quadrature points. This algebraic formulation automatically supports non-polynomial and non-interpolatory bases, thus is more general than the more common derivation in terms of Lagrange polynomials on the quadrature points.

Backends available in this release:

CEED resource (-ceed)

Backend

/cpu/self/blocked

Blocked reference implementation

/cpu/self/ref

Serial reference implementation

/cpu/self/tmpl

Backend template, defaults to /cpu/self/blocked

/cpu/occa

Serial OCCA kernels

/gpu/occa

CUDA OCCA kernels

/omp/occa

OpenMP OCCA kernels

/ocl/occa

OpenCL OCCA kernels

/gpu/magma

CUDA MAGMA kernels

Examples available in this release:

User code

Example

ceed

• ex1 (volume)

mfem

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

petsc

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

nek5000

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

## v0.21 (Sep 30, 2018)¶

A MAGMA backend (which relies upon the MAGMA package) was integrated in libCEED for this release. This initial integration set up the framework of using MAGMA and provided the libCEED functionality through MAGMA kernels as one of libCEED’s computational backends. As any other backend, the MAGMA backend provides extended basic data structures for , , and , and implements the fundamental CEED building blocks to work with the new data structures. In general, the MAGMA-specific data structures keep the libCEED pointers to CPU data but also add corresponding device (e.g., GPU) pointers to the data. Coherency is handled internally, and thus seamlessly to the user, through the functions/methods that are provided to support them.

Backends available in this release:

CEED resource (-ceed)

Backend

/cpu/self

Serial reference implementation

/cpu/occa

Serial OCCA kernels

/gpu/occa

CUDA OCCA kernels

/omp/occa

OpenMP OCCA kernels

/ocl/occa

OpenCL OCCA kernels

/gpu/magma

CUDA MAGMA kernels

Examples available in this release:

User code

Example

ceed

• ex1 (volume)

mfem

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

petsc

• BP1 (scalar mass operator)

nek5000

• BP1 (scalar mass operator)

## v0.2 (Mar 30, 2018)¶

libCEED was made publicly available the first full CEED software distribution, release CEED 1.0. The distribution was made available using the Spack package manager to provide a common, easy-to-use build environment, where the user can build the CEED distribution with all dependencies. This release included a new Fortran interface for the library. This release also contained major improvements in the OCCA backend (including a new /ocl/occa backend) and new examples. The standalone libCEED example was modified to compute the volume volume of a given mesh (in 1D, 2D, or 3D) and placed in an examples/ceed subfolder. A new mfem example to perform BP3 (with the application of the Laplace operator) was also added to this release.

Backends available in this release:

CEED resource (-ceed)

Backend

/cpu/self

Serial reference implementation

/cpu/occa

Serial OCCA kernels

/gpu/occa

CUDA OCCA kernels

/omp/occa

OpenMP OCCA kernels

/ocl/occa

OpenCL OCCA kernels

Examples available in this release:

User code

Example

ceed

• ex1 (volume)

mfem

• BP1 (scalar mass operator)

• BP3 (scalar Laplace operator)

petsc

• BP1 (scalar mass operator)

nek5000

• BP1 (scalar mass operator)

## v0.1 (Jan 3, 2018)¶

Initial low-level API of the CEED project. The low-level API provides a set of Finite Elements kernels and components for writing new low-level kernels. Examples include: vector and sparse linear algebra, element matrix assembly over a batch of elements, partial assembly and action for efficient high-order operators like mass, diffusion, advection, etc. The main goal of the low-level API is to establish the basis for the high-level API. Also, identifying such low-level kernels and providing a reference implementation for them serves as the basis for specialized backend implementations. This release contained several backends: /cpu/self, and backends which rely upon the OCCA package, such as /cpu/occa, /gpu/occa, and /omp/occa. It also included several examples, in the examples folder: A standalone code that shows the usage of libCEED (with no external dependencies) to apply the Laplace operator, ex1; an mfem example to perform BP1 (with the application of the mass operator); and a petsc example to perform BP1 (with the application of the mass operator).

Backends available in this release:

CEED resource (-ceed)

Backend

/cpu/self

Serial reference implementation

/cpu/occa

Serial OCCA kernels

/gpu/occa

CUDA OCCA kernels

/omp/occa

OpenMP OCCA kernels

Examples available in this release:

User code

Example

ceed

ex1 (scalar Laplace operator)

mfem

BP1 (scalar mass operator)

petsc

BP1 (scalar mass operator)