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**KINSOL** is a solver for nonlinear algebraic systems. It includes a Newton-Krylov solver as well as Picard and fixed point solvers, both of which can be accelerated with Anderson acceleration. KINSOL is based on the previous Fortran package NKSOL of Brown and Saad.

KINSOL’s Newton solver employs the Inexact Newton method. As this solver is intended mainly for large systems, four iterative methods are provided to solve the resulting linear systems–GMRES, Bi-CGStab, TFQMR, and FGMRES. These are Krylov methods, implemented with scaling and preconditioning, and can be used with all versions of the NVECTOR module.

For the sake of convenience to users with smaller systems, KINSOL (used with the serial NVECTOR module) also includes direct (dense, banded, and sparse) linear solvers for the linear systems. In this case the nonlinear iteration is a Modified Newton method.

In addition, KINSOL (used with the serial NVECTOR module) also includes interfaces to the sparse direct solvers, KLU, and the the multi-threaded sparse solver, SuperLU_MT.

In addition to the basic Krylov method modules, the KINSOL package includes a module called KINBBDPRE, which provides a band-block-diagonal preconditioner for the native MPI parallel vector.

For use with Fortran applications, a set of Fortran/C interface routines, called FKINSOL, is also supplied. These are written in C, but assume that the user calling program and all user-supplied routines are in Fortran.

See Software page for download and documentation.

## kinsol release history

### What’s new in v2.9.0?

- New features and/or enhancements
- Two new NVECTOR modules added: for Hypre ParVector and PETSc.
- In vector API, added new required function, N_VGetVectorID.
- Upgrades to sparse solver interfaces; now support CSR matrix type with KLU solver.
- Example codes were changed from using NV_DATA macro to using N_VGetArrayPointer_* when using the native vectors shipped with SUNDIALS.
- Updated to return integers from linear solver and preconditioner ‘free’ functions.
- Added FKINCREATE and FKININIT routines to split FKINMALLOC routine into two pieces. FKINMALLOC remains for backward compatibility, but documentation for it has been removed.
- Added kinFoodWeb_kry_omp.c OpenMP example.

- Bug fixes
- Fixed memory leak in banded preconditioner interface.
- Fixed some examples w.r.t. switch to new macro/function names SUNRexp etc.
- Various minor fixes to installation-related files.
- Corrected name N_VCloneEmptyVectorArray to N_VCloneVectorArrayEmpty in all documentation files.
- In FKINSOL, added missing Fortran interface routines so that users can supply the sparse Jacobian routine.
- Minor corrections and additions to User Guide, including removal of references to specific NVECTOR names in usage skeletons.
- Minor bug fix in Picard iteration so that newest iterate is returned.
- Minor bug fix in line search to prevent infinite loop when beta condition fails and lambda is below minimum size.

### What’s new in v2.8.0?

- New features
- Added fixed-point iteration and Picard iteration as globalization strategy options, both with Anderson acceleration.
- Added interface to the sparse direct solver KLU.
- Added interface to SuperLU_MT.
- Added interface to FGMRES.

- Bug fixes
- Corrected two return values in function KINStop.
- Fixed line setting smu in KINLapackBand.
- Fixed bug involving initialization of mxnewtstep.
- Fixed bug in difference quotient increments in kinDlsBandDQJac.
- Fixed an incorrect return value ier in FKINSOL function FKINfunc.

- Changes to the FKINSOL module
- In optional input routines FKINSETIIN, FKINSETRIN, and FKINSETVIN, removed the optional fourth argument key_length.
- Revised integer declarations in all examples so that those which must match a C type long int are declared INTEGER*8.

- Changes related to the build system
- Dropped support and documentation of the Autotools mode of installation.

### What’s new in v2.7.0?

- Bug fixes
- Three major logic bugs were fixed – involving updating the solution vector, updating the linesearch parameter, and a missing error return.
- Three minor errors were fixed – involving setting etachoice in the Matlab/KINSOL interface, a missing error case in KINPrintInfo, and avoiding an exponential overflow in the evaluation of omega.
- linear solver memory set to zero after being created.
- linear solver memory is freed on an error return.

- Changes to user interface
- Problem size and related integers (bandwidth parameters etc.) all have type long int, except for those in user calls specifying BLAS/LAPACK routines.

### What’s new in v2.6.0?

- New features
- new linear solver module, based on Blas and Lapack for both dense and banded matrices.

- Changes to user interface
- reorganization of all linear solver modules into two families (besides the existing family of scaled preconditioned iterative linear solvers, the direct solvers, including the new Lapack-based ones, were also organized into a direct family).
- maintaining a single pointer to user data, optionally specified through a Set-type function.
- general streamlining of the band-block-diagonal preconditioner module distributed with the solver.

### What’s new in v2.5.0?

- Changes related to the build system
- rearranged the entire SUNDIALS source tree.
- all exported header files are now installed in separate subdirectories of the installtion include directory.
- header files are included now by specifying the relative path (e.g. #include <kinsol/kinsol.h>).

### What’s new in v2.4.0?

- New features
- added direct linear solvers (dense and band, provided through the KINDENSE and KINBAND modules, respectively) thus adding modified (and exact) Newton methods to KINSOL.
- added KINSPBCG interface module to allow KINSOL to interface with the shared SPBCG (scaled preconditioned Bi-CGSTAB) linear solver module.
- added KINSPTFQMR interface module to allow KINSOL to interface with the shared SPTFQMR (scaled preconditioned TFQMR) linear solver module.
- added support for SPBCG and SPTFQMR to the KINBBDPRE preconditioner module.
- added option to KINBBDPRE preconditioner module to allow specification of different half-bandwidths for difference quotient approximation and retained matrix.
- added support for interpreting failures in user-supplied functions.

- Bug fixes
- corrected a bug in the preconditioner logic that caused the initial call to the preconditioner setup routine (controlled by KINSetNoInitSetup) to be skipped during subsequent calls to KINSol.

- Changes to underlying algorithm
- modified the KINBBDPRE preconditioner module to allow the use of different half-bandwidths for the difference quotient approximation and the retained matrix.
- added nonlinear residual monitoring scheme to control Jacobian updating when a direct linear solver is used (modified Newton iteration).

- Changes to user interface
- changed argument of KINFree and KINBBDPrecFree to be the address of the respective memory block pointer, so that its NULL value is propagated back to the calling function.
- modified the argument list of KINBBDPrecAlloc to allow specification of the upper and lower half-bandwidths to be used in the computation of the local Jacobian blocks (mudq, mldq), and the half-bandwidths of the retained banded approximation to the local Jacobian block (mukeep, mlkeep).
- added KINSPBCG module which defines appropriate KINSpbcg* functions to allow KINSOL to interface with the shared SPBCG linear solver module.
- added KINBBDSpbcg function to KINBBDPRE module to support SPBCG linear solver module.
- changed function type names to accomodate all the Scaled Preconditioned Iterative Linear Solvers now available:

KINSpgmrJactimesVecFn -> KINSpilsJacTimesVecFn

KINSpgmrPrecSetupFn -> KINSpilsPrecSetupFn

KINSpgmrPrecSolveFn -> KINSpilsPrecSolveFn - changed function types so that all user-supplied functions return an integer flag.
- changed some names for KINBBDPRE function outputs.
- added option for user-supplied error handler function.
- added option for user-supplied info handler function.
- renamed all exported header files (except for kinsol.h, all header files have the prefix kinsol_).
- changed naming scheme for KINSOL examples.

- Changes to FKINSOL module:
- modified argument list of FKINBBDINIT to accomadate changes made to KINBBDPRE module, so now user must specify the upper and lower half-bandwidths for the difference quotient approximation (mudq, mldq) and the retained matrix (mukeep, mlkeep).
- added support for KINSPBCG/SPBCG (added FKIN*SPBCG* functions).
- added support for KINSPTFQMR/SPTFQMR (added FKIN*SPTFQMR* functions).
- added support for KINDENSE/DENSE (added FKIN*DENSE* functions).
- added support for KINBAND/BAND (added FKIN*DENSE* functions).
- Optional inputs are now set using routines FKINSETIIN (integer inputs), FKINSETRIN (real inputs), and FKINSETVIN (vector inputs) through pairs key-value. Optional outputs are still obtained from two arrays (IOUT and ROUT), owned by the user and passed as arguments to FKINMALLOC.

- Changes related to the build system
- updated configure script and Makefiles for Fortran examples to avoid C++ compiler errors (now use CC and MPICC to link only if necessary).
- the main KINSOL header file (kinsol.h) is still exported to the install include directory. However, all other KINSOL header files are exported into a kinsol subdirectory of the install include directory.
- the KINSOL library now contains all shared object files (there is no separate libsundials_shared library any more).

### What’s new in v2.3.0?

- Changes to user interface
- KINSOL now stores an actual copy of the constraints vector rather than just a pointer in order to resolve potential scoping issues.
- several optional input functions were combined into a single function:

- KINSpgmrSetPrecSetupFn, KINSpgmrSetPrecSolveFn and KINSpgmrSetPrecData were combined into KINSpgmrSetPreconditioner

- KINSpgmrSetJacTimesVecFn and KINSpgmrSetJacData were combined into KINSpgmrSetJacTimesVecFn

- Changes to FKINSOL module:
- FKINSPGMRSETPSET and FKINSPGMRSETPSOL were combined into FKINSPGMRSETPREC.
- due to changes to the main solver, if FKPSOL is provided, then FKPSET must also be defined, even if it is empty.

### What’s new in v2.2.2?

- Bug fixes
- fixed bug in computation of the scaled step length.
- fixed bug in logic for disabling the call to the preconditioner setup function at the first iteration.

- Changes to documentation
- added section with numerical values of all input and output solver constants.

- Changes related to the build system
- fixed autoconf-related bug to allow configuration with the PGI Fortran compiler.
- modified to use customized detection of the Fortran name mangling scheme (autoconf’s AC_F77_WRAPPERS routine is problematic on some platforms).
- added –with-mpi-flags as a configure option to allow user to specify MPI-specific flags.
- updated Makefiles for Fortran examples to avoid C++ compiler errors (now use CC and MPICC to link).

### What’s new in v2.2.1?

- Changes related to the build system
- changed order of compiler directives in header files to avoid compilation errors when using a C++ compiler.
- changed method of generating sundials_config.h to avoid potential warnings of redefinition of preprocessor symbols.

### What’s new in v2.2.0?

- New feature
- added option to disable all error messages.

- Bug fixes
- fixed constraints-related bug.
- fixed bug in implementation of line-search method related to beta-condition.
- corrected value of ealpha variable (related to forcing term).

- Changes related to NVECTOR module
- removed machEnv, redefined table of vector operations (now contained in the N_Vector structure itself).
- all KINSOL functions create new N_Vector variables through cloning, using an N_Vector passed by the user as a template.

- Changes to type names and KINSOL constants
- removed type ‘integertype’; instead use ‘int’ or ‘long int’, as appropriate.
- restructured the list of return values from the various KINSOL functions.
- changed all KINSOL constants (inputs and return values) to have the prefix ‘KIN_’ (e.g. KIN_SUCCESS).
- renamed function type ‘SysFn’ to ‘KINSysFn’.

- Changes to underlying algorithms
- modified line-search backtracking scheme to use cubic interpolation after the first backtrack, if possible.
- changed implementation of constraints:

constraints[i] = 0 then u[i] NOT constrained

constraints[i] = +1 then u[i] >= 0

constraints[i] = -1 then u[i] <= 0

constraints[i] = +2 then u[i] > 0

constraints[i] = -2 then u[i] < 0

where u is the solution vector (see the KINSOL User Guide [1] for additional details).

- Changes to optional input/output
- added KINSet* and KINGet* functions for optional inputs/outputs, replacing the arrays iopt and ropt.
- added new optional inputs (e.g. maximum number of nonlinear iterations between calls to preconditioner setup routine, etc.).
- the value of the last return flag from any function within the SPGMR linear solver module can be obtained as an optional output using KINSpgmrGetLastFlag.

- Changes to user-callable functions
- added new function KINCreate which initializes the KINSOL solver object and returns a pointer to the KINSOL memory block.
- removed N (problem size) from all functions.
- shortened argument lists of most KINSOL functions (the arguments that were dropped can now be specified through KINSet* functions).
- removed reinitialization functions for SPGMR linear solver (same functionality can be obtained using KINSpgmrSet* functions).

- Changes to user-supplied functions
- removed N (problem dimension) from argument lists.
- in KINSPGMR, shortened argument lists for user preconditioner functions.