Add `cgls-shift` algorithm

tmigot commented 7 months ago

[x] Add a file cgls_lanczos_shift.jl in the folder src
[x] Add include("cgls_lanczos_shift.jl") in src/Krylov.jl
[x] Add a file test_cgls_lanczos_shift.jl in the folder test
[x] Add include("test_cgls_lanczos_shift.jl") in test/runtests.jl
[x] Add a CglsLanczosShiftSolver structure in src/krylov_solvers.jl
[x] Add export CglsLanczosShiftSolver in src/krylov_solvers.jl
[x] Update KRYLOV_SOLVERS in src/krylov_solvers.jl
[x] Update the loop for (KS, fun, nsol, ...) at the end of src/krylov_solvers.jl
[x] Add the docstring of CglsLanczosShiftSolver in docs/src/api.md (section Solver Types)
[x] Add @docs cgls_lanczos_shift cgls_lanczos_shift! in the most relevant markdown file of docs/src/solvers
[x] Add an allocation test for CGLS_LANCZOS_SHIFT in test/test_allocations.jl
[x] Add :cgls_lanczos_shift in test/test_mp.jl
[x] Add tests for CglsLanczosShiftSolver in test/test_solvers.jl
~Add a test for the warm-start feature of CGLS_LANCZOS_SHIFT in test/test_warm_start.jl~
[x] Add a test for the verbose mode of CGLS_LANCZOS_SHIFT in test/test_verbose.jl
[x] Add CGLS_LANCZOS_SHIFT in docs/src/preconditioners.md
[x] Add CGLS_LANCZOS_SHIFT in docs/src/processes.md
[x] Add CGLS_LANCZOS_SHIFT in docs/src/factorization-free.md (not needed for methods with multiple shifts)
[x] Add CGLS_LANCZOS_SHIFT in docs/src/storage.md
[x] Add a file cgls_lanczos_shift.md in the folder docs/src/examples and update docs/make.jl
[x] Add CglsLanczosShiftSolver in a note of docs/src/inplace.md if the solver requires the argument memory or nshifts
[x] Add a dispatch for solve! and cgls_lanczos_shift! in src/krylov_solve.jl