WebR — Análise de Fusão via HHI

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# ============================================
# Analise de fusao via HHI
# Simulacao de fusao horizontal
# ============================================

cat("====== ANALISE DE FUSAO VIA HHI ======\n\n")

# --- Mercado pre-fusao ---
# Market shares (%) de 6 firmas
shares <- c(30, 25, 18, 12, 10, 5)
nomes <- paste0("Firma ", LETTERS[1:6])

HHI_pre <- sum(shares^2)

cat("--- Mercado pre-fusao ---\n")
cat(sprintf("%-10s %s\n", "Firma", "Share (%)"))
cat(strrep("-", 22), "\n")
for (i in seq_along(shares)) {
  cat(sprintf("%-10s %5.1f%%\n", nomes[i], shares[i]))
}
cat(sprintf("\nHHI pre-fusao = %.0f\n", HHI_pre))

classif <- ifelse(HHI_pre < 1500, "Nao concentrado",
           ifelse(HHI_pre < 2500, "Moderadamente concentrado",
                  "Altamente concentrado"))
cat("Classificacao:", classif, "\n\n")

# --- Fusao: Firma A + Firma B ---
cat("--- Fusao: Firma A + Firma B ---\n")
shares_pos <- c(shares[1] + shares[2], shares[3:6])
nomes_pos <- c("A+B", nomes[3:6])
HHI_pos <- sum(shares_pos^2)
delta_HHI <- HHI_pos - HHI_pre

# Propriedade: delta_HHI = 2 * s_A * s_B
delta_formula <- 2 * shares[1] * shares[2]

cat(sprintf("%-10s %s\n", "Firma", "Share (%)"))
cat(strrep("-", 22), "\n")
for (i in seq_along(shares_pos)) {
  cat(sprintf("%-10s %5.1f%%\n", nomes_pos[i], shares_pos[i]))
}
cat(sprintf("\nHHI pos-fusao = %.0f\n", HHI_pos))
cat(sprintf("Delta HHI = %.0f\n", delta_HHI))
cat(sprintf("Verificacao: 2*s_A*s_B = 2*%d*%d = %.0f\n\n",
    shares[1], shares[2], delta_formula))

# --- Avaliacao CADE/DOJ ---
cat("--- Avaliacao antitruste ---\n")
if (HHI_pos >= 2500 & delta_HHI > 200) {
  cat("ALERTA: mercado altamente concentrado + delta > 200\n")
  cat("=> Fusao recebe escrutinio detalhado\n")
} else if (HHI_pos >= 1500 & delta_HHI > 100) {
  cat("ATENCAO: mercado moderadamente concentrado + delta > 100\n")
  cat("=> Fusao levanta preocupacoes\n")
} else {
  cat("OK: fusao provavelmente aprovada sem restricoes\n")
}

# --- Cenarios alternativos ---
cat("\n--- Cenarios alternativos de fusao ---\n")
cat(sprintf("%-12s %-10s %-10s %-10s\n",
    "Fusao", "HHI pos", "Delta", "Alerta?"))
cat(strrep("-", 45), "\n")

combos <- list(c(1,2), c(1,3), c(2,3), c(3,4), c(5,6))
for (combo in combos) {
  i <- combo[1]; j <- combo[2]
  s_new <- c(shares[i] + shares[j], shares[-c(i,j)])
  hhi_new <- sum(s_new^2)
  d_hhi <- hhi_new - HHI_pre
  alerta <- ifelse(hhi_new >= 2500 & d_hhi > 200, "SIM",
            ifelse(hhi_new >= 1500 & d_hhi > 100, "atencao", "nao"))
  cat(sprintf("%-12s %-10.0f %-10.0f %-10s\n",
      paste0(LETTERS[i], "+", LETTERS[j]), hhi_new, d_hhi, alerta))
}

# --- Grafico ---
par(mfrow = c(1, 2), mar = c(5, 4.5, 3, 1), bg = "#f8f9fa")

# Painel 1: Barras pre vs pos fusao
bp <- barplot(
  rbind(c(shares, 0), c(shares_pos, NA)),
  beside = TRUE,
  names.arg = c(nomes, ""),
  col = c("#0d6efd", "#dc3545"),
  main = "Market shares: pre vs. pos-fusao",
  ylab = "Share (%)", ylim = c(0, 60),
  las = 2, cex.names = 0.7)
legend("topright",
       legend = c("Pre-fusao", "Pos-fusao (A+B)"),
       fill = c("#0d6efd", "#dc3545"),
       cex = 0.65, bg = "white")

# Painel 2: HHI com faixas
hhi_vals <- c(HHI_pre, HHI_pos)
bp2 <- barplot(hhi_vals,
  names.arg = c("Pre-fusao", "Pos-fusao"),
  col = c("#0d6efd", "#dc3545"),
  main = paste0("HHI: Delta = +", delta_HHI),
  ylab = "HHI", ylim = c(0, max(HHI_pos) * 1.3))

# Faixas
abline(h = 2500, col = "#dc3545", lty = 2, lwd = 2)
abline(h = 1500, col = "#fd7e14", lty = 2, lwd = 2)
text(0.5, 2600, "Altamente concentrado", col = "#dc3545",
     cex = 0.65, font = 2, pos = 4)
text(0.5, 1600, "Moderadamente", col = "#fd7e14",
     cex = 0.65, font = 2, pos = 4)
text(bp2, hhi_vals + 80,
     labels = round(hhi_vals), font = 2, cex = 0.9)

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