MUMPS3

The MUMPS3 package provides a Julia interface with the MUMPS 5.2.0 parallel direct solver, used for solving A*x=y for square A (as well as some other functionality).

This package does not come with a distribution of MUMPS, and it is up to the user to provide a working MUMPS library (see MUMPS installation section).

Installation

Two things must be installed: MUMPS3.jl and MUMPS 5.2.0.

Installing MUMPS3.jl

The package is installed by entering the Pkg environment by typing ]add [email protected]:wrs28/MUMPS3.jl.git, which will looks like this:

(v1.1) pkg> add git@github.com:wrs28/MUMPS3.jl.git

Alternatively, it can be installed through the Pkg package:

using Pkg
Pkg.add("[email protected]:wrs28/MUMPS3.jl.git")

MUMPS3 will need to be told where the MUMPS library is via the environment variable ENV["MUMPS_PREFIX"], which defaults to

ENV["MUMPS_PREFIX"] = "/usr/local/opt/brewsci-mumps"

This must be set each time before loading the package. I recommend putting it in your startup.jl file by adding this line to ~/.julia/config/startup.jl

push!(ENV,"MUMPS_PREFIX"=>"/path/to/your/mumps/directory")

In addition to MUMPS.jl, you will need MPI.jl, via Pkg.add("MPI") or ]add MPI:

(v1.1) pkg> add MPI

Installing MUMPS 5.2.0 (mostly for OSX)

This can be a bit tricky. The source code can be downloaded here, but compiling and linking it into a dynamic library is awkward at best.

On Mac OS, there is an easy alternative from Homebrew, and detailed instructions can be found here. In short, the calls

$ brew tap brewsci/num
$ brew install brewsci-mumps

should be sufficient for installing mumps and its dependencies.

By default, this installs MUMPS and its dependencies in "/usr/local/opt/brewsci-mumps"

Getting Started

To load the package, simply call using MUMPS3. Additionally you will need to load MPI.jl by calling using MPI.

Before any calls to MUMPS3, you must initialize the MPI environment by calling MPI.Init(). If working in interactive mode, to avoid multiples MPI.Init calls, I recommend something like

MPI.Initialized() ? nothing : MPI.Init()

at the top of your code.

Basic Examples

using MUMPS3,MPI,LinearAlgebra,SparseArrays

MPI.Initialized() ? nothing : MPI.Init()

N, M = 1000, 10
A = sparse(I,N,N) + sprand(N,N,1/N)
y = sprand(N,M,1/sqrt(N*M))

x = mumps_solve(A,y)
norm(A*x-y) # should be ~1-e15

Goal and Design

The goal of this package is to provide simultaneously the full functionality and control that MUMPS 5.2.0 offers, while also providing intuitive high-level usage that requires next-to-no knowledge about the MUMPS API.

This is done by providing a Julia structure MumpsC{T} which exactly matches the [SDCZ]MUMPS_STRUC_C used inside the MUMPS C-interface.

Name

There are already two MUMPS pacakages called MUMPS.jl and MUMPS.jl, so the name-space seemed a bit crowded to me. I considered MMR as the solution to the MUMPS problem, but this nomenclature has some obvious problems. I'm open to any suggestions.

Basic Usage

There are five high-level functions that use the MUMPS library: mumps_solve, mumps_factorize, mumps_det, mumps_schur_complement, mumps_select_inv. The first three are self-explanatory, and last two compute the Schur complement matrix and select entries of the inverse, respectively. With the exception of mumps_factorize, all of these methods internally create and destroy their own mumps instances.

mumps_solve(A,y) -> x takes in a square matrix A and vector or matrix y and outputs x such that A*x=y.

mumps_factorize(A) -> LU does an LU factorization on A. The returned object is a Mumps object, and can be used with \, ldiv, and ldiv!, eg x=LU\y. This requires first loading LinearAlgebra: using LinearAlgebra.

mumps_det(A) -> d computes the determinant of A.

mumps_schur_complement(A,shur_inds) -> S computes the Schur complement S of A. The indices defining the Schur block are contained in schur_inds, either as an integer array or as a sparse matrix, the populated rows of which define the Schur variables.

mumps_select_inv(A,IJ) -> a⁻¹ and mumps_select_inv(A,I,J) -> a⁻¹ computes select elements of the inverse of A. IJ is a sparse matrix whose sparsity pattern defines which elements are computed. I, J are arrays of integers such that the kth linear index of a⁻¹ has the cartesian counterpart (I[k],J[k]).

Lower-level usage

The MUMPS3 package is build around the Mumps{T} structure, which contains MumpsC{T}, a structure which mirrors the [SDCZ]MUMPS_STRUC_C used inside the MUMPS library. For more control over how to access MUMPS, one can work directly with this structure.

Mumps(A; [sym, par=1]) -> mumps initializes a Mumps object with the same type as A. The sym argument can be passed explicitly, else it is determined from the symmetry and positive definiteness of A. See the MUMPS 5.2.0 documentation for what sym and par mean.

Mumps(A, y; [sym, par=1]) -> mumps initializes a Mumps object with the type determined by A and y, loaded with matrix A and right hand side y.

Mumps{T}(; sym=0, par=1)->mumps initializes a blank Mumps{T} instance.

mumps_solve(mumps) -> x solves for x, and both a matrix and rhs must have been previously provided to mumps. This can be done by initializing with A and y, or by using the provide_matrix! and provide_rhs! functions.

mumps_solve(mumps,y) -> x solves for x and provides mumps with the right hand side y.

mumps_factorize!(mumps) does and LU factorization on mumps in place.

mumps_det!(mumps) computes the determinant in mumps. The determinant can be accessed by subsequently calling det(mumps). This requires first loading LinearAlgebra: using LinearAlgebra.

mumps_schur_complement!(mumps,x) computes the Schur complement matrix, where the Schur indices are defined by x in the same way as for mumps_schur_complement (see above). The Schur complement can be subsequently accessed by get_schur_complement(mumps).

mumps_select_inv!(x,mumps) computes selected elements of the inverse of A (previously provided to mumps). The elements sought are determined from the sparsity pattern of x, which the results are also saved in.

There are also in-place versions of all of these (eg mumps_solve!(x,A,y), which is equivalent to ldiv!(x,A,y)). See the documentation, eg, ?mumps_solve! for more detail.

Accessing Mumps data

If not working with the highest level functions, it is often necessary to provide or retrieve data from Mumps{T}.

provide_matrix(mumps,A) gives the Mumps instance mumps the square matrix A. It attempts to convert A to a type consistent with mumps, throwing warnings when this happens.

provide_rhs!(mumps,y) gives the Mumps instance mumps the right hand side (matrix or vector) y. It attempts to convert y to a type consistent with mumps, throwing warnings when this happens.

get_rhs(mumps) -> y retrieves the right hand side from mumps, if available. get_rhs!(y,mumps) does the same thing in-place.

get_schur_complement(mumps) -> S retrieves the Schur complement matrix S from mumps, if available. get_schur_complement!(S,mumps) does the same thing in-place.

get_sol(mumps) -> x retrieves the solution x from mumps. MUMPS 5.1.2 could overwrite the rhs with the solution. I'm not sure if MUMPS 5.2.0 any longer does this. This function differs from get_rhs! because it returns always the solution data, which may or may not be the same as the rhs data (depending on whether rhs is sparse or not). get_sol!(x,mumps) does the same thing, in-place.

finalize!(mumps) frees the pointers contained therein for garbage collection. Its counterpart, initialize!(mumps) resets mumps.

Lowest Level Usage

For complete control over MUMPS, one can manipulate a Mumps{T} object directly. Be warned, this can expose unsafe operation which can crash Julia, if, for example, one attempts to access a finalized Mumps instance.

I recommend refering to the MUMPS documentation, Section 6.1 in particular.

Given a Mumps{T} object mumps, you can set the ICNTL integer array by set_icntl!(mumps,index,value). The current ICNTL can be viewed by display_icntl(mumps)

As indicated above, matrices and rhs's can be provided with provide_matrix! and provide_rhs!.

The JOB parameter can be set by set_job!(mumps,job).

A call to MUMPS can be made with invoke_mumps!(mumps).

Some convenience functions for changing INCTL are provided, though their documentation is not complete. For example, to set ICNTL to its default, call default_icntl!(mumps). To set the printing level, set_print_level!(mumps,level). To suppress printing entirely (except for errors) suppress_printing!(mumps) or suppress_display!(mumps).

List of Methods

low-level manipulation
invoke_mumps!(mumps)
set_icntl!(mumps,index,value; [displaylevel=1])
set_job!(mumps,job)

low-level access
provide_matrix!(mumps,A)
provide_rhs!(mumps,y)
get_rhs!(y,mumps)
get_rhs(mumps) -> y
get_schur_complement!(S,mumps)
get_schur_complement(mumps) -> S
get_sol!(x,mumps)
get_sol(mumps) -> x

Mumps initialization
Mumps{T}(;[sym=0, par=1]) -> mumps
Mumps(A; [sym, par=1]) -> mumps
Mumps(A,rhs; [sym, par=1]) -> mumps
initialize!(mumps)
finalize!(mumps)

Mumps solution
mumps_solve!(x,mumps)
mumps_solve!(x,A,y)
mumps_solve!(x,mumps,y)
mumps_solve(mumps) -> x
mumps_solve(A,y) -> x
mumps_solve(mumps,y) -> x
mumps_factorize!(mumps)
mumps_factorize(A) -> mumps
mumps_det!(mumps; discard=true)
mumps_det(A) -> det
mumps_schur_complement!(mumps, schur_inds)
mumps_schur_complement!(mumps, x)
mumps_schur_complement(A,schur_inds) -> S
mumps_schur_complement(A,x) -> S
mumps_select_inv!(x,mumps)
mumps_select_inv!(x,A)
mumps_select_inv(A,IJ::Sparse) -> A⁻¹
mumps_select_inv(A,I,J) -> A⁻¹

ICNTL manipulation
display_icntl(mumps)
set_error_stream!(mumps,stream)
set_diagnostics_stream!(mumps,stream)
set_info_stream!(mumps,stream)
set_print_level!(mumps,level)
suppress_printing!(mumps)
toggle_printing!(mumps)
sparse_matrix!(mumps)
dense_matrix!(mumps)
sparse_rhs!(mumps)
dense_rhs!(mumps)
toggle_null_pivot!(mumps)
transpose!(mumps)

LinearAlgebra extensions
det(mumps) -> det
\(mumps,y) = mumps\y -> x
ldiv(mumps,y) -> x
ldiv!(x,mumps,y)