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# question 1
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using Optim
f(x) = -x[1]^4-10x[1]^3-2x[1]^2-3x[1]-2
minusf(x) = x[1]^4+10x[1]^3+2x[1]^2+3x[1]+2
startval = rand(1)   # random starting value
result = optimize(minusf, startval, BFGS())


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# question 2
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using DataFrames
using CSV
using HTTP
url = "https://raw.githubusercontent.com/OU-PhD-Econometrics/fall-2020/master/ProblemSets/PS1-julia-intro/nlsw88.csv"
df = CSV.read(HTTP.get(url).body, DataFrame)
X = [ones(size(df,1),1) df.age df.race.==1 df.collgrad.==1]
y = df.married.==1

function ols(beta, X, y)
    ssr = (y.-X*beta)'*(y.-X*beta)
    return ssr
end

beta_hat_ols = optimize(b -> ols(b, X, y), rand(size(X,2)), LBFGS(), Optim.Options(g_tol=1e-6, iterations=100_000, show_trace=true))
println(beta_hat_ols.minimizer)

using GLM
bols = inv(X'*X)*X'*y
df.white = df.race.==1
bols_lm = lm(@formula(married ~ age + white + collgrad), df)


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# question 3
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function logit(alpha, X, d)

    # your turn

    return loglike
end

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# question 4
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# see Lecture 3 slides for example

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# question 5
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freqtable(df, :occupation) # note small number of obs in some occupations
df = dropmissing(df, :occupation)
df[df.occupation.==10,:occupation] .= 9
df[df.occupation.==11,:occupation] .= 9
df[df.occupation.==12,:occupation] .= 9
df[df.occupation.==13,:occupation] .= 9
freqtable(df, :occupation) # problem solved

X = [ones(size(df,1),1) df.age df.race.==1 df.collgrad.==1]
y = df.occupation

function mlogit(alpha, X, d)

    # your turn

    return loglike
end

