linear_steps.jl

"""
    Make a linear forward calculation
"""
function linear_forward(A, W, b)
    # Make a linear forward and return inputs as cache
    Z = (W * A) .+ b
    cache = (A, W, b)

    @assert size(Z) == (size(W, 1), size(A, 2))

    return (Z = Z, cache = cache)
end


"""
    Make a forward activation from a linear forward.
"""
function linear_forward_activation(A_prev, W, b, activation_function="relu")
    @assert activation_function ∈ ("sigmoid", "relu")
    Z, linear_cache = linear_forward(A_prev, W, b)

    if activation_function == "sigmoid"
        A, activation_cache = sigmoid(Z)
    end

    if activation_function == "relu"
        A, activation_cache = relu(Z)
    end

    cache = (linear_step_cache=linear_cache, activation_step_cache=activation_cache)

    @assert size(A) == (size(W, 1), size(A_prev, 2))

    return A, cache
end