# What is the best way to update matrix in callable function?
**URL:** https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641
**Category:** General Usage
**Tags:** question
**Created:** [July 22, 2022, 4:20pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641 "2022-07-22T16:20:27Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@Amro](https://discourse.julialang.org/u/Amro)
#### Post date: [July 22, 2022, 4:20pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/1 "2022-07-22T16:20:27Z")
I have a file called “run.jl” which has a function “update”. I have a main function which create matrix “Record”, which needs to be updated in a `for loop`. However, the matrix is not updated. What is the best way to update it with defining it as global variable?
```julia
#run.jl
function update(Record,iter)
Record += Record*iter;
end
# main code
include("run.jl");
select = true;
if select == true
Record = [1,2;3,4];
end
iter=0;
for _ in 1:100
iter += 1;
update(Record,iter)
end
```
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [July 22, 2022, 5:03pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/2 "2022-07-22T17:03:30Z")
The matrix `Record` is not updated, because you are not updating it.
> [@Amro](#):
>
> `Record += Record*iter;`
does not update `Record`, but instead creates a new matrix, which has a value equal to `Record + Record*iter`.
If you want to update it you must do it in-place, which you can achieve with `.=` (notice the dot):
```julia
Record .+= Record .* iter
```
But you could also write this as
```julia
Record .*= (1 + iter)
```
---
### Author:  [@Amro](https://discourse.julialang.org/u/Amro)
#### Post date: [July 22, 2022, 5:55pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/3 "2022-07-22T17:55:34Z")
I got it, thank you very much!
Given that:
```julia
Record = [1,2;3,4];
```
which method below is faster (In terms of performance):
```julia
for _ in 1:100
Record .= Record*iter + Record*50 ; # Method-1
Record[:] = Record[:]*iter + Record[:]*50; # Method-2
end
```
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [July 22, 2022, 6:03pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/4 "2022-07-22T18:03:51Z")
Neither of them is good. The last line is definitely bad, but also in the first one you forget dots, and do unnecessary operations.
> [@Amro](#):
>
> `Record .= Record*iter + Record*50`
should rather be
```julia
Record .= Record .* iter .+ Record .* 50
```
Make sure all dots are there.
But it’s better to do
```julia
Record .*= (iter + 50)
```
But you can replace the whole loop
> [@Amro](#):
>
> ```julia
> for _ in 1:100
> Record .= Record*iter + Record*50 ; # Method-1
> end
>
> ```
with
```julia
Record .*= float(iter + 50)^100
```
The use of `float` is to avoid integer overflow.
---
### Author:  [@Amro](https://discourse.julialang.org/u/Amro)
#### Post date: [July 22, 2022, 6:11pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/5 "2022-07-22T18:11:00Z")
Thank you!
Actually, I tried to shorten the scheme. The original is:
```julia
Record = [1,2;3,4];
SS = [3,4;5,6];
iter = 0;
for _ in 1:100
iter += 1;
Record .= Record .* iter .+ SS .* 50 ;
end
```
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [July 22, 2022, 6:13pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/6 "2022-07-22T18:13:29Z")
What is `iter`?
---
### Author:  [@Amro](https://discourse.julialang.org/u/Amro)
#### Post date: [July 22, 2022, 6:15pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/7 "2022-07-22T18:15:44Z")
I’ve corrected.
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [July 22, 2022, 7:18pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/8 "2022-07-22T19:18:03Z")
That’s a bit harder to simplify, at least for my vacation brain😎
But at least you can do
```julia
for iter in 1:100
```
instead of `iter += 1` inside the loop body.
---
### Author:  [@Amro](https://discourse.julialang.org/u/Amro)
#### Post date: [July 22, 2022, 7:30pm UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/9 "2022-07-22T19:30:46Z")
Lol, thank you. I really appreciate your help during vacation.
---
### Author:  [@acxz](https://discourse.julialang.org/u/acxz)
#### Post date: [July 23, 2022, 2:29am UTC](https://discourse.julialang.org/t/what-is-the-best-way-to-update-matrix-in-callable-function/84641/10 "2022-07-23T02:29:16Z")
For a solution to a similar problem to this see the following comment; [How to build this sparsematrix in Julia - #9 by acxz](https://discourse.julialang.org/t/how-to-build-this-sparsematrix-in-julia/84608/9)