Hi! I’m trying to find the trace of a matrix: `A = reshape(1:m*n,m,n)`

with `m=1000`

and `n=500`

, by writing `tr(A)`

which is what the documentation instructs. However, I get the following error:

**ERROR:** UndefVarError: `tr`

not defined

Stacktrace:

[1] top-level scope

I have no idea how to resolve this, as I thought the `tr`

function was basic to the language and I didn’t need to do anything beforehand to use it. Perhaps that’s where I am going wrong here.

I’d appreciate any help. Thank you!

Try searching the Julia documentation.

Try

```
julia> using LinearAlgebra
julia> x = randn(10,10)
julia> tr(x)
```

You need to first issue `using LinearAlgebra`

(which is its own module).

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Welcome to the discussion!

Sometimes, if you are just skimming the documentation online - you might notice at the top of the page it will say something like “Standard Library / Linear Algebra.” The folks writing the examples in the page often don’t issue `using LinearAlgebra`

, since they assume you have arrived at the page looking for the documentation for the package.

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