title: Julia ERROR: UndefVarError: σ not defined
body: <p>I am running this from julia: </p>
  
  <pre><code>W1 = param(rand(3, 5))
  b1 = param(rand(3))
  layer1(x) = W1 * x .+ b1
  W2 = param(rand(2, 3))
  b2 = param(rand(2))
  
  layer2(x) = W2 * x .+ b2
  model(x) = layer2(σ.(layer1(x)))
  
  model(rand(5))
  </code></pre>
  
  <p>I am getting this error:</p>
  
  <pre><code>ERROR: UndefVarError: σ not defined
  Stacktrace:
  [1] model(::Array{Float64,1}) at ./REPL[35]:1
  </code></pre>
  
  <p>I dont understand the error. I am new to julia. Please help me out here. I am following this tutorial: <a href="https://fluxml.github.io/Flux.jl/stable/models/basics.html#Taking-Gradients-1" rel="nofollow noreferrer">https://fluxml.github.io/Flux.jl/stable/models/basics.html#Taking-Gradients-1</a></p>
  
  <p>Thank you.</p>