Groups   178 of 99+      julia-users › Overriding Methods in Base 9 posts by 3 authors      Jared Crean    8 11 15   For a problem I am working on, I need to be able to store explicit zeros in a SparseMatrixCSC.  While the storage format supports this, the setindex! method does not. Also, for banded sparse matricies I can define a much more efficient getindex method than the generic one.  When I define my own method  importing the one from Base and then creating a method with the same signature as the existing one  I get warnings of the type:   Warning: Method definition getindex Base.SparseMatrix.SparseMatrixCSC  T :Any, Ti :Integer , Integer, Integer  in module SparseMatrix at sparse sparsematrix-jl:1232 overwritten in module PDESolverCommon at  users creanj .julia v0.4 PDESolverCommon src sparse-jl:63.  My question is in what contexts is the method overwritten?  In my local context  the REPL session where I use the one I created .  Do functions within Base use the one in Base or the local one?  Jared Crean       Yichao Yu    8 11 15    Every user of it  including Base  in your current julia session.        Jared Crean            Jared Crean    8 11 15   Thanks for the quick reply.  Now I am curious, what happens if the old method was inlined in a function compiled before the new method was created.  It must continue to use the old method, right?  What if the function was not inlined?  for example:  mat     create SparseMatrixCSC here function calcSomething A::SparseMatrixCSC     x   A i,j  + 1     ... end  calcSomething mat   function getindex A::SparseMatrixCSC, i, j      define new getindex here end  calcSomething mat     what happens?   I understand that overriding methods in Base is playing with fire...    Jared Crean      Yichao Yu    8 11 15   On Tue, Aug 11, 2015 at 4:42 PM, Jared Crean  jcre... gmail.com  wrote:    Thanks for the quick reply.       Now I am curious, what happens if the old method was inlined in a function    compiled before the new method was created.  It must continue to use the old    method, right?  What if the function was not inlined?       for example:       mat     create SparseMatrixCSC here    function calcSomething A::SparseMatrixCSC        x   A i,j  + 1       ...    end       calcSomething mat        function getindex A::SparseMatrixCSC, i, j         define new getindex here    end       calcSomething mat     what happens?          I understand that overriding methods in Base is playing with fire...   Currently basically an undefined behavior.  https:  github.com julialang julia issues 265       Tony Kelman    8 11 15   For storing explicit zeros you're best off modifying nzvals directly.  In what way are you specializing your banded getindex method? Is this a classical banded but dense-within-the-band matrix, or general CSC sparse but with additional knowledge that no nonzeros ever have i and j different by more than the bandwidth? You're probably better off either making a new type for this that just wraps a SparseMatrixCSC for storage and either stores or is parameterized by the bandwidth, or using a different method other than getindex for this. If you'll miss the syntax, you could write a macro to locally replace getindex with your specialized version.      Jared Crean    8 11 15   Its a classical dense-within-the-band matrix  from a Finite Element problem .  I want access to the solvers that are already supported by SparseMatrixCSC, and interfacing them to another new type seems like a lot of work.  If there were an abstract CSC matrix type, this could be made much easier.  I've been hoping issues  8001,  9906, and  9928 would lead in that direction, but so far they haven't.  The syntax is really what I am after with the overriding of the methods.  Using a macro is a safer alternative.  I'll have to try that at some point.  Jared Crean      Tony Kelman    8 11 15   If it's dense within the band, then what you really want is issue 8240. Are you dealing with symmetric positive definite, symmetric indefinite, or nonsymmetric? Eigenproblems or linear system solves? There are LAPACK methods for banded matrices that should be more efficient than using Cholmod or UMFPACK here, since they don't need to do anywhere near as much integer arithmetic as SuiteSparse would  to represent a band matrix in CSC format . We just don't have a Julia type for band matrices yet or ccall wrappers around the corresponding LAPACK methods. I'm not sure whether Jiahao made much progress on any prototypes, but banded matrices could easily be worked on outside of base at first.      Jared Crean    8 11 15   Its a nonsymmetric linear solve.  Issue 8240 looks great, FE problems will be much easier to do when that is finished.  I am working on a large  eventually parallel  CFD solver that will use Petsc  I'm working on wrappers here:  https:  github.com JaredCrean2 PETSc-jl  for the linear solves.  UMPFPACK is sufficiently efficient for debugging and running small, single processor problems.  Jared Crean      Tony Kelman    8 11 15   For single-node work, gbtrf and gbtrs are your friends here. Apparently we do have those wrapped in base linalg lapack-jl already, but there are no tests for them right now, and no higher-level lufact to connect them to owing to the lack of a banded type.