# Vector of vector of gradients
**URL:** https://discourse.julialang.org/t/vector-of-vector-of-gradients/113348
**Category:** Numerics
**Tags:** question
**Created:** [April 22, 2024, 4:35pm UTC](https://discourse.julialang.org/t/vector-of-vector-of-gradients/113348 "2024-04-22T16:35:56Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Domenico\_Lahaye](https://discourse.julialang.org/u/Domenico_Lahaye)
#### Post date: [April 22, 2024, 4:35pm UTC](https://discourse.julialang.org/t/vector-of-vector-of-gradients/113348/1 "2024-04-22T16:35:56Z")
I am to extend the scalar case of a gradient of a function, i.e.,
```julia
foo = Vector{Function}(undef,2)
gnu = Vector{Function}(undef,2)
foo[1] = (x,y) -> x+y
foo[2] = (x,y) -> x-y
A = [1. 2.; 3. 4.]
gnu = (x,y) -> B * [foo[1](x,y),foo[2](x,y)]
```
to the case of a vector of gradient of functions
```julia
ndof = 3
foo = Vector{Vector}(undef,ndof)
gnu = Vector{Vector}(undef,ndof)
for i=1:ndof
foo[i] = Vector{Function}(undef,2)
gnu[i] = Vector{Function}(undef,2)
end
foo[1][1] = (x,y) -> x+y
foo[1][2] = (x,y) -> x-y
foo[2][1] = (x,y) -> 2*x+2*y
foo[2][2] = (x,y) -> 2*x-2*y
foo[3][1] = (x,y) -> 3*x+3*y
foo[3][2] = (x,y) -> 3*x-3*y
A = [1. 2.; 3. 4.]
for i=1:ndof
gnu[i][:] .= (x,y) -> A * [foo[i][1](x,y);foo[i][2](x,y)]
end
```
Help is appreciated.
---
### Author:  [@gdalle](https://discourse.julialang.org/u/gdalle)
#### Post date: [April 22, 2024, 5:22pm UTC](https://discourse.julialang.org/t/vector-of-vector-of-gradients/113348/2 "2024-04-22T17:22:36Z")
Is there something that doesn’t work with your code? Why do you need help?
As a side note, a `Vector{Function}` has an abstract element type and so it might be rather slow. Depending on your specific problem, a more appropriate structure can speed things up (for instance if all your functions are linear combinations you can store the coefficients instead of the anonymous function objects)
---
### Author:  [@Domenico\_Lahaye](https://discourse.julialang.org/u/Domenico_Lahaye)
#### Post date: [April 22, 2024, 6:37pm UTC](https://discourse.julialang.org/t/vector-of-vector-of-gradients/113348/3 "2024-04-22T18:37:08Z")
@gdalle : thx!
The code works indeed. I was testing incorrectly.
I will worry about performance later.