All of the examples can be found in Jupyter notebook form here.

Huber regression

This example can be found here: https://web.stanford.edu/~boyd/papers/pdf/cvx_applications.pdf. Here we set big_example = false to only generate a small example which takes less time to run.

big_example = false
if big_example
    n = 300
    number_tests = 50
else
    n = 50
    number_tests = 10
end
10

Generate data for Huber regression.

using Random
Random.seed!(1);
number_samples = round(Int,1.5*n);
beta_true = 5*randn(n);
X = randn(n, number_samples);
Y = zeros(number_samples);
v = randn(number_samples);
# Generate data for different values of p.
# Solve the resulting problems.
using Convex, SCS, Distributions
lsq_data = zeros(number_tests);
huber_data = zeros(number_tests);
prescient_data = zeros(number_tests);
p_vals = range(0, stop=0.15, length=number_tests);
for i=1:length(p_vals)
    p = p_vals[i];
    # Generate the sign changes.
    factor = 2 * rand(Binomial(1, 1-p), number_samples) .- 1;
    Y = factor .* X' * beta_true + v;

    # Form and solve a standard regression problem.
    beta = Variable(n);
    fit = norm(beta - beta_true) / norm(beta_true);
    cost = norm(X' * beta - Y);
    prob = minimize(cost);
    solve!(prob, () -> SCS.Optimizer(verbose=0));
    lsq_data[i] = evaluate(fit);

    # Form and solve a prescient regression problem,
    # i.e., where the sign changes are known.
    cost = norm(factor .* (X'*beta) - Y);
    solve!(minimize(cost), () -> SCS.Optimizer(verbose=0))
    prescient_data[i] = evaluate(fit);

    # Form and solve the Huber regression problem.
    cost = sum(huber(X' * beta - Y, 1));
    solve!(minimize(cost), () -> SCS.Optimizer(verbose=0))
    huber_data[i] = evaluate(fit);
end
┌ Warning: Problem status ALMOST_OPTIMAL; solution may be inaccurate.
└ @ Convex ~/work/Convex.jl/Convex.jl/src/solution.jl:250
using Plots

plot(p_vals, huber_data, label="Huber", xlabel="p", ylabel="Fit" )
plot!(p_vals, lsq_data, label="Least squares")
plot!(p_vals, prescient_data, label="Prescient")
# Plot the relative reconstruction error for Huber and prescient regression,
# zooming in on smaller values of p.
indices = findall(p_vals .<= 0.08);
plot(p_vals[indices], huber_data[indices], label="Huber")
plot!(p_vals[indices], prescient_data[indices], label="Prescient")

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