# Changelog of SLEPc versions

## [3.25] - 2026-03-31

### Added

- `EPS`: new structured eigenvalue problem type `EPS_LREP` for the Linear Response
  Eigenvalue Problem, see `MatCreateLREP()`.
- New context destroy functions `EPSSetArbitrarySelectionContextDestroy()` and
  `STShellSetDestroy()`.
- Typing stubs for the Python extension module `slepc4py.SLEPc`.

### Changed

- When using polynomial filters (`STFILTER`), the stopping test now allows specifying
  a number of eigenvalues (`nev`) if one does not really want to compute all the
  eigenvalues lying in the interval.
- A new argument "destroy" (a routine for destroying the context) has been added to
  `DSNEPSetComputeMatrixFunction()`.

## [3.24] - 2025-09-30

### Added

- `STFILTER`: new polynomial filter based on a truncated Chebyshev series. Use
  `STFilterSetType()` to choose among the available filters.
- `EPS`: new structured eigenvalue problem type `EPS_HAMILT` for the case of a matrix
   with Hamiltonian structure created with `MatCreateHamiltonian()`.

### Removed

- The interface to TRLAN has been removed since it is no longer available for download.

## [3.23] - 2025-03-29

### Added

- `SVD`: new support for a stopping test based on a threshold, so that it is possible
  to compute singular values based on how they decay until a certain limit, without
  knowing a priori how many will be finally obtained. See `SVDSetThreshold()`.
- `EPS`: similar threshold stopping test for eigenvalues, see `EPSSetThreshold()`.
- New interface to external package ChASE for standard Hermitian eigenproblems.

### Changed

- The Fortran interface has been updated, following the changes in PETSc. Now it is
  fully compatible with Fortran 90 using modules. The compiler will check the type
  of arguments when calling subroutines, including enumerates, as well as in other
  parts of the code. The Fortran interface is no longer generated with `bfort`.

## [3.22] - 2024-09-29

### Added

- `EPS`: added support for structured eigenvalue problems in the Krylov-Schur solver.
  In particular, the problem type `EPS_BSE` is intended to solve eigenproblems with
  Bethe-Salpeter structure, whose matrix has been created with `MatCreateBSE()`.
- `BV`: new function `BVGetSplitRows()` to split a `BV` row-wise using index sets.
- Added support for AMD GPUs via HIP and ROCm, see section 8.3 of the Users Manual.

### Changed

- Some interface functions now support `PETSC_CURRENT` to preserve the current value of
  the arguments. This implies that `PETSC_DEFAULT` is deprecated for setting a default
  value in those cases, and `PETSC_DETERMINE` or `PETSC_DECIDE` should be used instead.
  This is the case of, e.g., `EPSSetDimensions()`.
- `DS`: various improvements including optimization of memory usage.
- In slepc4py now `EPS.getEigenpair()` and `EPS.getEigenvalue()` will return a real value
  instead of a complex, if the problem is of Hermitian or generalized Hermitian type.

## [3.21] - 2024-03-30

### Added

- `ST`: new function `STShellSetApplyHermitianTranspose()` and other improvements for handling
  the conjugate transpose of the operator.

### Changed

- `SVDGetSignature()` now takes a `Vec` argument instead of `Vec*`. The former interface
  could not be used from Fortran.

## [3.20] - 2023-09-29

### Changed

- `BV`: now most `BV` implementations use the concept of leading dimension for internal
  storage. The implication of this is that codes relying on `BVGetArray()` must be
  adapted to use the value of the leading dimension, which may be different from the
  local number of rows. Use `BVGetLeadingDimension()` for this purpose.
- `BV`: now the default `BV` type is `BVMAT` instead of `BVSVEC`. This change should not
  affect application code.

## [3.19] - 2023-03-31

### Added

- New `DSHSVD` type for the hyperbolic SVD.
- Support for the hyperbolic SVD (HSVD) in the `SVDTRLANCZOS` solver.
- Add interface to dense SVD solvers in the external package KSVD.

## [3.18] - 2022-10-01

### Added

- `SVD`: add scaling parameter in thick-restart Lanczos for the GSVD, and also enable
  one-sided orthogonalization for GSVD.
- `SVD`: support for the hyperbolic SVD (HSVD), with a signature matrix passed with
  `SVDSetSignature()`.
- `FN`: add support for matrix function computation on the GPU, whenever the `Mat`
  arguments of `FNEvaluateFunctionMat()` are of type `MATSEQDENSECUDA` (and similarly
  for `FNEvaluateFunctionMatVec()`).
- `DS`: new functions `DSGetMatAndColumn()`/`DSRestoreMatAndColumn()`.

### Changed

- In configure, now the arguments intended to store link flags (and libraries) instead of
  being represented as comma-separated lists should be specified via a quoted string, e.g.,
  `--with-arpack-lib="-L/opt/soft/arpack -Wl,-rpath,/opt/soft/arpack -lparpack -larpack"`.
- Interface of `BVMatLanczos()` changed to receive a `Mat` instead of pointers, in a
  similar way to `BVMatArnoldi()`.
- `DS`: now every call to `DSGetMat()` must be paired with a call to `DSRestoreMat()`, it
  is not longer possible to just `MatDestroy()` the matrix.

### Removed

- Remove python2 support, python-3.4+ is now required.
- `DS`: remove `DSCopyMat()`.

## [3.17] - 2022-03-31

### Added

- `NEP`: user-defined preconditioner for the split form, see `NEPSetSplitPreconditioner()`.
  Support for preconditioner matrix different from the function matrix has also been
  improved for the callback interface.
- Add support for split preconditioner in `EPS` and `PEP` via `STSetSplitPreconditioner()`.

### Changed

- In C programs, instead of using `CHKERRQ()`, the recommended way of doing error
  checking is wrapping with `PetscCall()`, for instance, `PetscCall(EPSSolve(eps))`.
  `CHKERRQ()` will continue to work as before. In Fortran, error checking has not changed.
- `SVD`: clarify convergence test for GSVD, now the default is relative to the matrix norms,
  and relative to the singular value is not allowed.

## [3.16] - 2021-09-30

### Added

- `SVD`: support for the GSVD in `SVDTRLANCZOS`, `SVDCROSS` and `SVDCYCLIC` solvers.
- `NEP`: the `NEPCISS` solver (that was deprecated in version 3.14) has been recovered
  and enriched with a new Rayleigh-Ritz variant that is used by default now, see
  `NEPCISSSetExtraction()`. It now also supports subcommunicators.
- `PEP`: new solver `PEPCISS` with similar functionality as `NEPCISS`.
- Fortran: add support for ``SlepcInitialize(filename,help,ierr)``, ``SlepcInitialize(ierr)``
  in addition to current ``SlepcInitialize(filename,ierr)``.
- New `DSGSVD` type for the generalized SVD.
- New contour integral method in `DSNEP`.
- New function `BVSetRandomSign()` for random values equal to -1 or 1 with equal probability.
- New functions `RGIsAxisymmetric()`, `RGCanUseConjugates()` and `RGComputeQuadrature()`.
- New function `SlepcHasExternalPackage()` to check whether SLEPc was configured with the
  given external package.

### Changed

- `DSSetDimensions()` now has one argument less. Use `DSSVDSetDimensions()` to specify
  the number of columns in `DSSVD`. And similarly for `DSGSVD`.
- One of the `DS` matrices has been renamed from `DS_MAT_VT` to `DS_MAT_V` since it is
  no longer transposed.
- Interface of `BVMatArnoldi()` changed to receive a `Mat` instead of a pointer.
- `STShellGetContext()` now takes `void*` as return argument, as well as `XXXGetMonitorContext()`.
- Rename `BVMultInPlaceTranspose()` to `BVMultInPlaceHermitianTranspose()` to be
  consistent with PETSc naming convention.

### Removed

- The interface to BLZPACK has been removed since it is no longer available for download.

## [3.15] - 2021-03-31

### Added

- `SVD`: support for the GSVD added. This implies changes in the interface, e.g.,
  `SVDSetOperators()` should be used instead of `SVDSetOperator()`. New functions have
  been added such as `SVDSetProblemType()` and `SVDIsGeneralized()`.
- `SVD`: New solver `SVDRANDOMIZED`.
- `EPS`: New interface to external package EVSL.
- Import SLEPc4py sources into SLEPc source tree.
- New function `EPSKrylovSchurGetKSP()` to extract the `KSP` object used in the case
  of spectrum slicing runs. This allows setting MUMPS options even with partitions.
- New tolerance to check a definite inner product, see `BVSetDefiniteTolerance()`.
- New function `STSetPreconditionerMat()` to pass the matrix for building the
  preconditioner.
- New function `BVSetRandomNormal()` for random initial vectors with normal distribution.
- New function `DSGetTruncateSize()` to be used with `DSTruncate()`.

### Changed

- Configure option `--download-slepc4py` renamed to `--with-slepc4py`.
- `EPSLANCZOS` now requires that `EPSLanczosSetReorthog()` is called explicitly, or the
  corresponding command-line option is given. The intention is that inexperienced users
  realize that they should use `EPSKRYLOVSCHUR` instead of `EPSLANCZOS`.
- `ST`: now the coefficient/preconditioner matrix has the same prefix as the `KSP` object,
  so setting MUMPS options in the command-line requires the appropriate prefix, e.g.,
  `-st_mat_mumps_icntl_13 1`.
- `DSTruncate()` now has an additional argument `trim`.
- Monitors have been reorganized as in PETSc. Now use `-eps_monitor draw::draw_lg`
  instead of `-eps_monitor_lg`.

### Deprecated

- `STPrecondSetMatForPC()` is superseded by `STSetPreconditionerMat()`.

## [3.14] - 2020-09-30

### Added

- Add interfaces to dense eigensolvers and SVD solvers in ScaLAPACK, ELPA and Elemental.
- Reintroduce interface to FEAST external solver via MKL.
- New configure option `--download-slepc4py`.
- New functions `BVNormalize`, `VecCheckOrthonormality`, `STApplyMat`, `STMatMatSolve`.

### Changed

- `EPSLOBPCG` and `EPSCISS` now use `MatProduct()`/`KSPMatSolve()` instead of
  `MatMult()`/`KSPSolve()`.
- Rename `XXXReasonView()` to `XXXConvergedReasonView()`, and `XXXReasonViewFromOptions()`
  to `XXXConvergedReasonViewFromOptions()`.

### Deprecated

- The `NEPCISS` solver has been deprecated and will be completely removed in future versions.

## [3.13] - 2020-03-31

### Added

- `EPS`: new solver `lyapii` (Lyapunov inverse iteration) to compute rightmost eigenvalues.
- `NEP`: add a two-sided version of SLP.
- New functions: `EPSSetLeftInitialSpace()`, `MFNSolveTranspose()`.
- Interface to `PCHPDDM` and `KSPHPDDM` using `--download-hpddm`.

### Changed

- `configure`: the options `--with-xxx-flags` have been renamed to `--with-xxx-lib` (see
  `./configure --help`).
- `STGetOperator()` now has to be used with `STRestoreOperator()`.
- Now the arrays returned by `RGPolygonGetVertices()` must be freed by the user.

## [3.12] - 2019-09-30

- `ST`: now the default is to use Cholesky instead of LU if the problem matrices are `SBAIJ` or the
  user flags them as symmetric.
- Removed interface to external solver FEAST.
- Removed support for CMake and legacy builds.

## [3.11] - 2019-03-29

- `EPS`: reintroduce support for computing left eigenvectors, see `EPSSetTwoSided()`.
- `PEP`: enable JD solver in real arithmetic.
- `PEP`: spectrum slicing can now be used with symmetric non-hyperbolic problems.
- `NEP`: support for automatic determination of singularities in NLEIGS with the AAA algorithm.
- `NEP`: support for left eigenvectors and approximation of the resolvent.
- `FN`: implemented matrix logarithm.
- Enable compilation with non-GNU compilers in Windows platforms.
- Added support for `DESTDIR` in prefix install.

## [3.10] - 2018-09-18

- `NEP`: add support for deflation in SLP, RII and NArnoldi solvers.
- `FN`: improved matrix function evaluation of Phi functions.
- Interface changes: `PEPLinearSetCompanionForm()` has been deprecated, use
  `PEPLinearSetLinearization()` instead.

## [3.9] - 2018-04-12

- `PEP`: add spectrum slicing for Hermitian quadratic eigenvalue problems via STOAR.
- `PEP`: add support for non-monomial bases in JD.
- `BV`: add `BVTENSOR` to represent subspace bases with compact representation $`V = (I \otimes U) S`$.
- `BV`: improved implementation of block orthogonalization, including TSQR and SVQB.
- `BV`: add `BVGetSplit()` operation to split a given `BV` object in two.

## [3.8] - 2017-10-20

- Released under 2-clause BSD license.
- New solver class `LME` for linear matrix equations (such as Lyapunov or Sylvester) whose
  solution has low rank.
- `NEP`: added specific support for rational eigenvalue problems with `NEPSetProblemType()`.
- Added nonlinear inverse iteration as an option of `EPSPOWER`.
- Added a preliminary implementation of polynomial filters in `STFILTER` to compute interior
  eigenvalues of symmetric problems without factorizing a matrix.
- `SVD`: add wrapper to PRIMME SVD solver.
- Improved evaluation of matrix functions, both in `FN` and `MFN`.
- GPU support improved in all solver classes.
- Simplified Fortran usage as in PETSc.
- Interface changes: `DSNormalize()` has been removed; `NEPInterpolSetDegree()` has been
  renamed to `NEPInterpolSetInterpolation()`, and takes an additional argument.

## [3.7] - 2016-05-16

- `NEP`: new solver `nleigs` that implements a (rational) Krylov method operating on a
  companion-type linearization of a rational interpolant of the nonlinear function.
- `PEP`: the `jd` solver can now compute more than one eigenpair.
- `MFN`: added a new solver `krylov` that works for different functions, not only the exponential.
  The solver available in previous versions has been renamed to `expokit`.
- `EPS`: in spectrum slicing in multi-communicator mode now it is possible to update the problem
  matrices directly on the sub-communicators.
- `EPS`: the contour integral solver now provides Chebyshev quadrature rule and Hankel extraction;
  all options are documented in STR-11.
- Now most solvers allow a user-defined criterion to stop iterating based on a callback function.
- Optimized solution of linear systems in Newton refinement for `PEP` and `NEP`.
- Added download option for most external packages.
- GPU support updated to use `VECCUDA` instead of `VECCUSP`, now including complex scalars.
- Interface changes: `EPS_CONV_EIG` has been renamed to `EPS_CONV_REL`;
  `BVAXPY()` has been removed, use `BVMult()` instead;
  `BVSetRandom()` no longer takes a `PetscRandom` argument, use `BVSetRandomContext()` instead.

## [3.6] - 2015-06-12

- New `EPS` solver: locally optimal block preconditioned conjugate gradient (LOBPCG).
- New `PEP` solvers: Jacobi-Davidson (JD), and symmetric TOAR (STOAR).
- New `NEP` solver: contour integral spectrum slice (CISS).
- Improved BLOPEX interface by adding hard locking. Now the user can specify the block size.
- Spectrum slicing in `EPS` can now be run in multi-communicator mode, where each process group
  computes a sub-interval.
- Added functions and command-line options to view the computed solution after solve, e.g.
  `-eps_view_vectors binary:myvecs.bin`
- The `MFN` solver class now takes an `FN` object to define the function. The functionality for
  computing functions of small, dense matrices has been moved from `DS` to `FN`.
  `MFNSetScaleFactor()` has been removed, now this scale factor must be specified in `FN`.
- `FN` now allows the definition of functions by combining two other functions.
- Added two new `RG` regions: `ring` a stripe along an ellipse with optional start and end angles;
  `polygon` an arbitrary polygon made up of a list of vertices.
- User makefiles must now include `${SLEPC_DIR}/lib/slepc/conf/slepc_common`.
- Interface changes: `EPSComputeRelativeError()` and `EPSComputeResidualNorm()` have been
  deprecated (use `EPSComputeError()` instead); the same for `PEP`, `NEP` and `SVD`;
  `PEPSetScale()` now allows passing two `Vec`s for diagonal scaling; `XXXPrintSolution()` has
  been replaced with `XXXErrorView()`; `STGetOperationCounters()` has been removed, its
  functionality is available via the log summary and with `KSPGetTotalIterations()`;
  `BVGetVec()` has been renamed to `BVCreateVec()`; the interface for defining `FN` functions of
  rational type has changed; `BVSetOrthogonalization()` takes one more argument.

## [3.5] - 2014-07-29

- A new solver class `PEP` for polynomial eigenvalue problems has been added. It replaces the
  former `QEP` class, that has been removed. `PEP` contains a new solver TOAR that can handle
  polynomials of arbitrary degree. Q-Lanczos has been removed since it did not have guaranteed
  stability.
- New `NEP` solver: polynomial interpolation using `PEP`.
- Added Newton iterative refinement in both `PEP` and `NEP`.
- A new auxiliary class `RG` allows the user to define a region in the complex plane. This can
  be used for filtering out unwanted eigenvalues in `EPS` and `PEP`.
- The auxiliary object `IP` has been removed and a new object `BV` has been added that subsumes
  its functionality.
- Support for requesting left eigenvectors has been removed, since none of the solvers were
  computing them internally.
- The `STFOLD` spectral transformation has been removed. Example `ex24.c` reproduces this
  functionality.
- Interface changes: `SVDSetTransposeMode()` has been renamed to `SVDSetImplicitTranspose()`;
  in `STSHIFT` the sign of sigma is the opposite to previous versions; `EPSJDSetBOrth()` now takes
  a boolean argument instead of an enum.

## [3.4] - 2013-07-05

- Added new class of solvers `NEP` for the nonlinear eigenvalue problem.
- Added new class of solvers `MFN` for computing the action of a matrix function on a vector.
- New `EPS` solver: Contour integral spectrum slice (CISS). Allows to compute all eigenvalues
  inside a region.
- New `QEP` solver: Q-Lanczos is a specialized variant of Q-Arnoldi for problems with symmetric
  matrices.
- Added support for shift-and-invert in `QEP`.
- Added a new auxiliary class `FN`: Mathematical Function, to be used in the definition of
  nonlinear eigenproblems.
- Added interface to external solver FEAST.
- Changed options `-xxx_monitor_draw` to `-xxx_monitor_lg`, and similarly for `-xxx_monitor_draw_all`.

## [3.3] - 2012-08-03

- New `EPS` solver: Rayleigh quotient conjugate gradient (RQCG). This is the first CG-type
  eigensolver in SLEPc. It can be used for computing smallest eigenvalues of symmetric-definite
  matrix pairs without inverting any matrix (a preconditioner can be used instead).
- Added a customizable parameter to specify how to restart in Krylov-Schur, see
  `EPSKrylovSchurSetRestart`. Tuning this parameter may speed up convergence significantly in
  some cases.
- Added support for generalized symmetric-indefinite eigenproblems in Krylov-Schur and the Davidson
  solvers. To use this, set the problem type to `EPS_GHIEP`.
- New variant of Generalized Davidson for generalized eigenproblems that expands the subspace with
  two vectors (GD2). It can be activated with `-eps_gd_double_expansion`.
- Added experimental support for arbitrary selection of eigenpairs, where the solver chooses the
  most wanted ones based on a user-defined function of the eigenvectors rather than simply sorting
  the eigenvalues.
- Added a new auxiliary class `DS`: Direct Solver (or Dense System), which is intended for
  developers rather than normal users.

## [3.2] - 2011-10-28

- Computational intervals for symmetric eigenproblems, that activate a spectrum slicing mechanism
  to obtain all eigenvalues in a given interval, see `EPSSetInterval()`.
- Partial support (experimental) for GPU computing via PETSc's `VECCUSP` and `MATAIJCUSP`.
- Improved performance and robustness of GD and JD solvers in (generalized) Hermitian problems.
- Performance improvement of solvers with explicit matrix such as `SVDCYCLIC` and `QEPLINEAR`
  (now use matrix preallocation).
- Added Matlab interface.
- Added support for parallel builds with CMake.
- Added support for quad precision (configure PETSc `--with-precision=__float128` with gcc-4.6 or
  later).
- Interface changes: now all `XXXDestroy()` routines take a pointer to the object.

## [3.1] - 2010-08-04

- New `EPS` solvers: Generalized Davidson (GD) and Jacobi-Davidson (JD). These are the first
  eigensolvers in SLEPc that belong to the class of preconditioned eigensolvers.
- Added a new instance of `ST` called `STPRECOND`. This is not really a spectral transformation
  but rather a convenient way of handling the preconditioners in the new eigensolvers.
- Added a new class `QEP` for solving quadratic eigenvalue problems. Currently, it contains two
  solvers: the Q-Arnoldi method and another one that provides a linearization of the problem and
  then invokes an eigensolver from `EPS`.
- Added support for balancing of non-Hermitian problems, see `EPSSetBalance()`.
- Improved sorting of eigenvalues, now with the possibility of sorting with respect to a target
  value. With shift-and-invert, now the ordering of eigenvalues is the expected one, relative to
  the target. Also added support for user-defined orderings, see `EPSSetWhichEigenpairs()`.
- Added support for user-defined convergence tests, see `EPSSetConvergenceTest()`. Several
  predefined convergence criteria are available. Also, there is a new flag for computing the true
  residual for the convergence test, see `EPSSetTrueResidual()`.
- Monitors have been reorganized and now more possibilities are available.
- Changes in user interface: `EPSAttachDeflationSpace()` has been renamed to `EPSSetDeflationSpace()`,
  `EPSSetLeftVectorsWanted()` replaces `EPSSetClass()` for requesting left eigenvectors; Change in
  arguments: `EPSSetDeflationSpace()`; Deprecated function: `EPSSetInitialVector()`, replaced by
  `EPSSetInitialSpace()`; `STSINV` has been renamed to `STSINVERT`.

## [3.0.0] - 2009-02-04

- Released under GNU LGPL license.
- Improved support for the case that many eigenpairs are to be computed. This is especially so in
  the default eigensolver (Krylov-Schur) for symmetric problems, as well as for SVD computations. The
  user can control the behavior of the solver with a new parameter `mpd`, see `EPSSetDimensions()`.
- Support for harmonic projection in the default eigensolver (Krylov-Schur), see `EPSSetExtraction()`.
  This can be useful for computing interior or rightmost eigenvalues without the need of a spectral
  transformation.
- Memory usage has been optimized in most solvers. In some cases, memory requirements have been
  halved with respect to the previous versions.
- In the spectral transformations (`ST`) the linear solver used internally has been changed to a
  direct solver by default. The user can still employ an iterative linear solver by setting the
  appropriate options.
- Added better support for Fortran 90.
- Improved support for `make install`.

## [2.3.3] - 2007-06-01

- A new solver class `SVD` has been introduced for computing the singular value decomposition of
  a rectangular matrix. The structure of this new type is very similar to that of `EPS`, and it
  simplifies the computation of singular values and vectors.
- Better support for generalized problems. Eigenvector purification has been added to improve
  accuracy in the case of generalized eigenproblems with singular B. Also, a new problem type
  (`EPS_PGNHEP`) has been added for better addressing generalized problems in which A is non-Hermitian
  but B is Hermitian and positive definite.
- Now `make install` is available thus facilitating system-wide installation.

## [2.3.2] - 2006-10-02

- A new `krylovschur` eigensolver has been added, that implements the Krylov-Schur method. This
  method is related to the Arnoldi and Lanczos algorithms, but incorporates a new restarting scheme
  that makes it competitive with respect to implicit restart. This eigensolver is now the default
  for both symmetric and non-symmetric problems.
- A new wrapper has been developed to interface with the PRIMME library. This library provides
  Davidson-type eigensolvers.
- The `lanczos` solver has been improved, in particular, the different reorthogonalization
  strategies are now more robust.
- Now the `arnoldi` eigensolver supports the computation of eigenvalues other than those of largest
  magnitude.
- `EPSGetLinearIterations()` has been replaced with `EPSGetOperationCounters()`, providing more
  statistics about the solution process.
- `EPSGetIterationNumber()` now returns the number corresponding to outer iterations.
- The `lobpcg` wrapper has been renamed to `blopex`.
- The `planso` wrapper has been removed since PLANSO is no longer being distributed.

## [2.3.1] - 2006-03-03

- New variant of the Arnoldi method added to the `arnoldi` eigensolver (with delayed
  reorthogonalization, see `EPSArnoldiSetDelayed()`).
- Several optimizations for improving performance and scalability, in particular the
  orthogonalization steps.

## [2.3.0] - 2005-06-30

- New `lanczos` eigensolver, an explicitly restarted version of the Lanczos method for symmetric
  eigenproblems. Allows the user to choose among 5 reorthogonalization strategies.
- New spectrum folding spectral transformation.
- New configuration system, similar to PETSc's `configure.py`.
- New interface to an external eigensolver: LOBPCG implemented in Hypre.
- Added graphical convergence monitor (with `-eps_xmonitor`).
- Improvement of Arnoldi solver in terms of efficiency and robustness.
- Now the `lapack` solver uses specific Lapack routines for symmetric and generalized problems.
- Bug fix in the ARPACK interface.

## [2.2.1] - 2004-08-21

- The `power` eigensolver has been replaced by a simpler implementation.
- The `rqi` eigensolver has been removed. Now the Rayleigh Quotient Iteration is embedded in the
  `power` method.
- The `subspace` eigensolver has been rewritten. Now it follows the SRRIT implementation, which is
  much faster than the old one.
- The `arnoldi` eigensolver has been re-implemented as well. The new implementation is much more
  robust and efficient.
- A new Spectral Transformation (`ST`) has been added: the generalized Cayley transform.
- Support for user-provided deflation subspaces has been added, see `EPSAttachDeflationSpace()`.
- Support for preservation of symmetry in eigensolvers. For this feature, the user must explicitly
  call `EPSSetProblemType()` in symmetric problems.
- The two types of monitors (error estimates and values) have been merged in a single one.
- New function `EPSGetInvariantSubspace()`.
- Better support for spectrum slicing in `blzpack`.

## [2.2.0] - 2004-04-13

- `EPSSolve()` does not return the number of iterations. Use `EPSGetIterationNumber()` for this
  purpose.
- `EPSGetSolution()` has been replaced by `EPSGetEigenpair()` with a cleaner interface.
- `EPSComputeError()` has been replaced by `EPSComputeRelativeError()` and `EPSComputeResidualNorm()`
  with better error computing for zero eigenvalues. These functions now are oriented to single
  eigenpairs, as well as `EPSGetErrorEstimate()`.
- The possibilities of `EPSSetWhichEigenpairs()` have been reduced and now are more coherent across
  problem types.
- Removed `STNONE` spectral transformation. The default of `STSHIFT` with 0 shift is equivalent.
- Added `STSinvertSetMatStructure()` to optimize performance of `MatAXPY()` in shift-and-invert
  transformation.
- Classical and modified Gram-Schmidt orthogonalization use iterative refinement, with user options
  for parameter adjustment.

[unreleased]: https://gitlab.com/slepc/slepc/-/tree/main
[3.25]: https://gitlab.com/slepc/slepc/-/tree/release
[3.24]: https://gitlab.com/slepc/slepc/-/tree/release-3.24
[3.23]: https://gitlab.com/slepc/slepc/-/tree/release-3.23
[3.22]: https://gitlab.com/slepc/slepc/-/tree/release-3.22
[3.21]: https://gitlab.com/slepc/slepc/-/tree/release-3.21
[3.20]: https://gitlab.com/slepc/slepc/-/tree/release-3.20
[3.19]: https://gitlab.com/slepc/slepc/-/tree/release-3.19
[3.18]: https://gitlab.com/slepc/slepc/-/tree/release-3.18
[3.17]: https://gitlab.com/slepc/slepc/-/tree/release-3.17
[3.16]: https://gitlab.com/slepc/slepc/-/tree/release-3.16
[3.15]: https://gitlab.com/slepc/slepc/-/tree/release-3.15
[3.14]: https://gitlab.com/slepc/slepc/-/tree/release-3.14
[3.13]: https://gitlab.com/slepc/slepc/-/tree/release-3.13
[3.12]: https://gitlab.com/slepc/slepc/-/tags/v3.12
[3.11]: https://gitlab.com/slepc/slepc/-/tags/v3.11
[3.10]: https://gitlab.com/slepc/slepc/-/tags/v3.10
[3.9]: https://gitlab.com/slepc/slepc/-/tags/v3.9
[3.8]: https://gitlab.com/slepc/slepc/-/tags/v3.8
[3.7]: https://gitlab.com/slepc/slepc/-/tags/v3.7
[3.6]: https://gitlab.com/slepc/slepc/-/tags/v3.6
[3.5]: https://gitlab.com/slepc/slepc/-/tags/v3.5
[3.4]: https://gitlab.com/slepc/slepc/-/tags/v3.4
[3.3]: https://gitlab.com/slepc/slepc/-/tags/v3.3
[3.2]: https://gitlab.com/slepc/slepc/-/tags/v3.2
[3.1]: https://gitlab.com/slepc/slepc/-/tags/v3.1
[3.0.0]: https://gitlab.com/slepc/slepc/-/tags/v3.0.0
[2.3.3]: https://gitlab.com/slepc/slepc/-/tags/v2.3.3
[2.3.2]: https://gitlab.com/slepc/slepc/-/tags/v2.3.2
[2.3.1]: https://gitlab.com/slepc/slepc/-/tags/v2.3.1
[2.3.0]: https://gitlab.com/slepc/slepc/-/tags/v2.3.0
[2.2.1]: https://gitlab.com/slepc/slepc/-/tags/v2.2.1
[2.2.0]: https://gitlab.com/slepc/slepc/-/tags/v2.2.0
