# In matlab, we calculate inv(A)\* B by A\\B. How about Julia? note that A&B are two large sparse matrices
**URL:** https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322
**Category:** New to Julia
**Tags:** question
**Created:** [September 30, 2019, 12:26pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322 "2019-09-30T12:26:38Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@NITISH\_KUMAR](https://discourse.julialang.org/u/NITISH_KUMAR)
#### Post date: [September 30, 2019, 12:26pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/1 "2019-09-30T12:26:38Z")
Does anybody have experience with the calculation of inv(A)\*B in Julia, where A and B are large sparse matrices?
When I used zz = A\B in Julia. It shows the following error in Julia
````julia
MethodError: no method matching ldiv!(::SuiteSparse.UMFPACK.UmfpackLU{Float64,Int64}, ::SparseArrays.SparseMatrixCSC{Float64,Int64})
Closest candidates are:
ldiv!(!Matched::Number, ::AbstractArray) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\generic.jl:152
ldiv!(!Matched::LinearAlgebra.LU{T,LinearAlgebra.Tridiagonal{T,V}}, ::Union{AbstractArray{T,2}, AbstractArray{T,1}} where T) where {T, V} at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\lu.jl:523
ldiv!(!Matched::LinearAlgebra.Transpose{#s617,#s616} where #s616<:LinearAlgebra.LU{T,LinearAlgebra.Tridiagonal{T,V}} where #s617, ::Union{AbstractArray{T,2}, AbstractArray{T,1}} where T) where {T, V} at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\lu.jl:555
...
Stacktrace:
[1] \(::SuiteSparse.UMFPACK.UmfpackLU{Float64,Int64}, ::SparseArrays.SparseMatrixCSC{Float64,Int64}) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\factorization.jl:87
[2] \(::SparseArrays.SparseMatrixCSC{Float64,Int64}, ::SparseArrays.SparseMatrixCSC{Float64,Int64}) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.2\SparseArrays\src\linalg.jl:1374
[3] top-level scope at In[5]:1
```
````
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [September 30, 2019, 12:31pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/2 "2019-09-30T12:31:13Z")
Just make `B` dense? The result will be a dense matrix of that size anyway.
---
### Author:  [@NITISH\_KUMAR](https://discourse.julialang.org/u/NITISH_KUMAR)
#### Post date: [September 30, 2019, 12:55pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/3 "2019-09-30T12:55:23Z")
Thank you 🙂 I’ll try. Wondering if full() command is not supported in Julia 1.2?
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [September 30, 2019, 1:07pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/4 "2019-09-30T13:07:10Z")
> [@NITISH\_KUMAR](#):
>
> Wondering if full() command is not supported in Julia 1.2?
You can just do `Matrix(B)`.
---
### Author:  [@NITISH\_KUMAR](https://discourse.julialang.org/u/NITISH_KUMAR)
#### Post date: [September 30, 2019, 1:12pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/5 "2019-09-30T13:12:28Z")
Unfortunately, Same error.
MethodError: no method matching ldiv!(::SuiteSparse.UMFPACK.UmfpackLU{Float64,Int64}, ::SparseArrays.SparseMatrixCSC{Float64,Int64})
Closest candidates are:
ldiv!(!Matched::Number, ::AbstractArray) at C:\cygwin\home\Administrator\buildbot\worker\package\_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\generic.jl:152
ldiv!(!Matched::LinearAlgebra.LU{T,LinearAlgebra.Tridiagonal{T,V}}, ::Union{AbstractArray{T,2}, AbstractArray{T,1}} where T) where {T, V} at C:\cygwin\home\Administrator\buildbot\worker\package\_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\lu.jl:523
ldiv!(!Matched::LinearAlgebra.Transpose{#s617,#s616} where #s616\<:LinearAlgebra.LU{T,LinearAlgebra.Tridiagonal{T,V}} where #s617, ::Union{AbstractArray{T,2}, AbstractArray{T,1}} where T) where {T, V} at C:\cygwin\home\Administrator\buildbot\worker\package\_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\lu.jl:555
…
Stacktrace:
[1] (::SuiteSparse.UMFPACK.UmfpackLU{Float64,Int64}, ::SparseArrays.SparseMatrixCSC{Float64,Int64}) at C:\cygwin\home\Administrator\buildbot\worker\package\_win64\build\usr\share\julia\stdlib\v1.2\LinearAlgebra\src\factorization.jl:87
[2] (::SparseArrays.SparseMatrixCSC{Float64,Int64}, ::SparseArrays.SparseMatrixCSC{Float64,Int64}) at C:\cygwin\home\Administrator\buildbot\worker\package\_win64\build\usr\share\julia\stdlib\v1.2\SparseArrays\src\linalg.jl:1374
[3] top-level scope at In[5]:1
---
### Author:  [@Sukera](https://discourse.julialang.org/u/Sukera)
#### Post date: [September 30, 2019, 1:45pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/6 "2019-09-30T13:45:03Z")
> [@NITISH\_KUMAR](#):
>
> MethodError: no method matching ldiv!(::SuiteSparse.UMFPACK.UmfpackLU{Float64,Int64}, ::SparseArrays.SparseMatrixCSC{Float64,Int64})
Looks like you’re stll calling `ldiv!` with the sparse matrix 🤔
Can you show the code that produces this error?
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [September 30, 2019, 1:45pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/7 "2019-09-30T13:45:09Z")
Can you give an example of what you are doing?
```julia
julia> A = lu(sprand(5,5,0.5) + I)
UMFPACK LU Factorization of a (5, 5) sparse matrix
Ptr{Nothing} @0x00007fbedec06620
julia> B = sprand(5,5,0.4);
julia> A \ Matrix(B)
5Ă—5 Array{Float64,2}:
-0.247253 -0.458155 0.331186 -0.179299 0.222382
-0.812489 -2.25484 1.4221 -0.251258 1.58024
1.17403 2.29645 -0.930615 0.164422 -1.03411
0.338484 0.0 0.0 0.0 0.0
-0.18574 -0.0906186 0.0367224 0.660449 0.844956
```
---
### Author:  [@NITISH\_KUMAR](https://discourse.julialang.org/u/NITISH_KUMAR)
#### Post date: [September 30, 2019, 2:41pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/8 "2019-09-30T14:41:57Z")
I tried with another problem, it worked. However, stucked with the memory issue.
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [September 30, 2019, 3:02pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/9 "2019-09-30T15:02:54Z")
Yes, it would require a lot of memory to store that. What is the reason for doing this computation though? If this is some type of discretized problem where K is a “stiffness matrix” and M a “mass matrix” then I don’t see why you are doing K \ M.
---
### Author:  [@NITISH\_KUMAR](https://discourse.julialang.org/u/NITISH_KUMAR)
#### Post date: [September 30, 2019, 3:19pm UTC](https://discourse.julialang.org/t/in-matlab-we-calculate-inv-a-b-by-a-b-how-about-julia-note-that-a-b-are-two-large-sparse-matrices/29322/10 "2019-09-30T15:19:08Z")
Developing formulation for modal reduction in Multiphysics problems. It works in matlab if I consider both matrix as sparse and implement K \ M .