# Question about Julia zeros matrix?
**URL:** https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350
**Category:** General Usage
**Created:** [May 20, 2022, 6:39am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350 "2022-05-20T06:39:45Z")
**Posts on this page:** 13
**Page:** 1
### Author:  [@Raymond](https://discourse.julialang.org/u/Raymond)
#### Post date: [May 20, 2022, 6:39am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/1 "2022-05-20T06:39:45Z")
Dear all,
In matlab, we can add complex values into zeros matrix, but in Julia I cannot .Can you help me to modify my codes to add complex values into zeros matrix in Julia?
This is the matlab code.
```julia
>> A = zeros(2, 2)
A =
0 0
0 0
>> A(1, 1) = 1 + i
A =
1.0000 + 1.0000i 0.0000 + 0.0000i
0.0000 + 0.0000i 0.0000 + 0.0000i
```
And this the Julia codes, but it get an error.
```julia
julia> A = zeros(3, 3)
3×3 Matrix{Float64}:
0.0 0.0 0.0
0.0 0.0 0.0
0.0 0.0 0.0
julia> A[1, 1] = 1 + im
ERROR: InexactError: Float64(1 + 1im)
Stacktrace:
[1] Real
@ ./complex.jl:44 [inlined]
[2] convert
@ ./number.jl:7 [inlined]
[3] setindex!(::Matrix{Float64}, ::Complex{Int64}, ::Int64, ::Int64)
@ Base ./array.jl:905
[4] top-level scope
@ REPL[24]:1
```
Any help will be appreciated.
---
### Author:  [@liuyxpp](https://discourse.julialang.org/u/liuyxpp)
#### Post date: [May 20, 2022, 6:46am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/2 "2022-05-20T06:46:08Z")
Maybe you want this?
```julia
julia> A = zeros(Complex, 3, 3);
julia> A[1,1] = 1 + im
3×3 Matrix{Complex}:
1+1im 0+0im 0+0im
0+0im 0+0im 0+0im
0+0im 0+0im 0+0im
```
---
### Author:  [@Raymond](https://discourse.julialang.org/u/Raymond)
#### Post date: [May 20, 2022, 6:48am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/3 "2022-05-20T06:48:54Z")
I try to modify the Julia code like below, is it right?
```julia
julia> A = convert(Array{Any}, zeros(2, 2))
2×2 Matrix{Any}:
0.0 0.0
0.0 0.0
julia> A[1, 1] = 1 + im
1 + 1im
julia> A
2×2 Matrix{Any}:
1+1im 0.0
0.0 0.0
```
---
### Author:  [@liuyxpp](https://discourse.julialang.org/u/liuyxpp)
#### Post date: [May 20, 2022, 6:50am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/4 "2022-05-20T06:50:54Z")
The matrix contains elements of mixed types. It generally will deteriorate your performance.
---
### Author:  [@sostock](https://discourse.julialang.org/u/sostock)
#### Post date: [May 20, 2022, 7:00am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/5 "2022-05-20T07:00:44Z")
> [@liuyxpp](#):
>
> `julia> A = zeros(Complex, 3, 3);`
Since `Complex` is not a concrete type, this will also give you bad performance. Use `zeros(Complex{Float64}, 3, 3)` instead.
---
### Author:  [@liuyxpp](https://discourse.julialang.org/u/liuyxpp)
#### Post date: [May 20, 2022, 7:02am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/6 "2022-05-20T07:02:34Z")
Sure, you are right. My bad.
---
### Author:  [@Raymond](https://discourse.julialang.org/u/Raymond)
#### Post date: [May 20, 2022, 7:12am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/7 "2022-05-20T07:12:06Z")
@liuyxpp @sostock Thanks so much. It solves my problem.
---
### Author:  [@Raymond](https://discourse.julialang.org/u/Raymond)
#### Post date: [May 20, 2022, 7:25am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/8 "2022-05-20T07:25:58Z")
@liuyxpp @sostock I have another question. How can I transform this matlab code into Julia.
```matlab
>> val = zeros(3, 3);
>> row = zeros(3, 3);
>> A = [1 2 3; 6 5 1; 1 7 4]
A =
1 2 3
6 5 1
1 7 4
[val(1, :), row(1, :)] = max(A)
val =
6 7 4
0 0 0
0 0 0
row =
2 3 3
0 0 0
0 0 0
```
---
### Author:  [@liuyxpp](https://discourse.julialang.org/u/liuyxpp)
#### Post date: [May 20, 2022, 7:48am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/9 "2022-05-20T07:48:33Z")
I then suggest reading this part of doc carefully [Noteworthy Differences from other Languages · The Julia Language](https://docs.julialang.org/en/v1/manual/noteworthy-differences/#Noteworthy-differences-from-MATLAB). And learn Julia Array syntax from the beginning. Otherwise, your question list will continue to grow.
---
### Author:  [@Raymond](https://discourse.julialang.org/u/Raymond)
#### Post date: [May 20, 2022, 8:01am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/10 "2022-05-20T08:01:59Z")
Thanks for your suggetion. I will read it.
---
### Author:  [@jishnub](https://discourse.julialang.org/u/jishnub)
#### Post date: [May 20, 2022, 8:46am UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/11 "2022-05-20T08:46:32Z")
You probably want something like
```julia
julia> A
3×3 Matrix{Int64}:
1 2 3
6 5 1
1 7 4
julia> vals, inds = findmax(A, dims=1)
([6 7 4], CartesianIndex{2}[CartesianIndex(2, 1) CartesianIndex(3, 2) CartesianIndex(3, 3)])
```
The indices are `CartesianIndex`es, which are essentially `(row, col)` pairs. To obtain the row coordinates, you may use
```julia
julia> first.(Tuple.(inds))
1×3 Matrix{Int64}:
2 3 3
```
---
### Author:  [@Raymond](https://discourse.julialang.org/u/Raymond)
#### Post date: [May 21, 2022, 8:31pm UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/12 "2022-05-21T20:31:22Z")
@jishnub
Thanks for your help. I have another problem .How can I use `LinearIndices` to get the index. In matlab, we can use `sub2ind` .The matlab code is below.
```julia
>> A = [1 2 1; 2 2 1]
A =
1 2 1
2 2 1
>> inds = sub2ind([2,2], A(1,:), A(2,:))
inds =
3 4 1
```
---
### Author:  [@jishnub](https://discourse.julialang.org/u/jishnub)
#### Post date: [May 22, 2022, 3:06pm UTC](https://discourse.julialang.org/t/question-about-julia-zeros-matrix/81350/13 "2022-05-22T15:06:58Z")
The way to do this is to create a list of indices as `CartesianIndex(rowind, colind)` pairs. In this case, we may broadcast `CartesianIndices` over a list of row and column indices (Tuples, instead of creating a matrix as in Matlab).
```julia
julia> cartinds = CartesianIndex.((1,2,1), (2,2,1))
(CartesianIndex(1, 2), CartesianIndex(2, 2), CartesianIndex(1, 1)
```
After this, we create a list of all linear indices of a 2x2 matrix:
```julia
julia> lininds = LinearIndices((2,2))
2×2 LinearIndices{2, Tuple{Base.OneTo{Int64}, Base.OneTo{Int64}}}:
1 3
2 4
```
Finally, we index into `lininds` at the indices that we want.
```julia
julia> [lininds[i] for i in cartinds]
3-element Vector{Int64}:
3
4
1
```