WebR — Decisão de Operar ou Fechar

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# ============================================
# Decisao de Shutdown: tres regimes de preco
# CT(q) = 72 + 10q + 0.5q^2 (Ex. Resolvido 12.2)
# ============================================

CF <- 72
a <- 10; b <- 0.5

CT   <- function(q) CF + a*q + b*q^2
CV   <- function(q) a*q + b*q^2
CMg  <- function(q) a + 2*b*q
CMe  <- function(q) CF/q + a + b*q
CVMe <- function(q) a + b*q

# Pontos criticos
cvme_min <- a   # CVMe min (q -> 0+ para funcao crescente)
cme_min_q <- sqrt(CF / b)
cme_min <- CMe(cme_min_q)

# Tres cenarios de preco
precos <- c(30, 16, 8)
nomes <- c("Lucro positivo", "Prejuizo (opera)", "Fecha")
cores <- c("#198754", "#fd7e14", "#dc3545")

cat("====== TRES REGIMES DE PRECO ======\n")
cat("CT(q) =", CF, "+", a, "q +", b, "q^2\n")
cat("CVMe_min =", cvme_min, " | CMe_min =", round(cme_min, 2),
    " (em q =", round(cme_min_q, 2), ")\n\n")

for (i in 1:3) {
  p <- precos[i]
  cat("--- Preco p =", p, "---\n")

if (p < cvme_min) {
    cat("  p < CVMe_min => FECHAR (q = 0)\n")
    cat("  Lucro = -CF = -", CF, "\n\n")
  } else {
    q_s <- (p - a) / (2*b)
    lucro_op <- p * q_s - CT(q_s)
    lucro_fecha <- -CF
    cat("  q* =", round(q_s, 2), "\n")
    cat("  Lucro operando  =", round(lucro_op, 2), "\n")
    cat("  Lucro fechando  = -CF = -", CF, "\n")
    cat("  Decisao:", ifelse(lucro_op >= lucro_fecha, "OPERAR", "FECHAR"), "\n")
    if (p >= cme_min) cat("  Regime: LUCRO POSITIVO\n\n")
    else cat("  Regime: PREJUIZO (mas menor que CF)\n\n")
  }
}

# --- Grafico ---
par(mar = c(4.5, 4.5, 3, 2), bg = "#f8f9fa")
q_seq <- seq(0.5, 30, length = 500)

plot(q_seq, CMg(q_seq), type = "l", lwd = 3, col = "#dc3545",
     xlab = "q", ylab = "$/unidade",
     main = "Tres regimes de preco",
     ylim = c(0, 35), xlim = c(0, 30), cex.lab = 1.1)
lines(q_seq, CMe(q_seq), lwd = 2, col = "#0d6efd")
lines(q_seq, CVMe(q_seq), lwd = 2, col = "#198754", lty = 2)

# Linhas de preco e zonas
for (i in 1:3) {
  abline(h = precos[i], col = cores[i], lwd = 1.5, lty = 3)
  text(28, precos[i] + 0.8, paste0("p=", precos[i], ": ", nomes[i]),
       col = cores[i], cex = 0.7, font = 2, adj = 1)
}

# Zona verde (lucro)
rect(0, cme_min, 30, 35, col = rgb(0.1, 0.53, 0.33, 0.05), border = NA)
# Zona amarela (opera com prejuizo)
rect(0, cvme_min, 30, cme_min, col = rgb(0.99, 0.49, 0.05, 0.08), border = NA)
# Zona vermelha (fecha)
rect(0, 0, 30, cvme_min, col = rgb(0.86, 0.21, 0.27, 0.08), border = NA)

# Anotacoes das zonas
text(1, (cme_min + 35)/2, "Lucro > 0", col = "#198754", cex = 0.7, font = 3, adj = 0)
text(1, (cvme_min + cme_min)/2, "Prejuizo\n(opera)", col = "#fd7e14", cex = 0.65, font = 3, adj = 0)
text(1, cvme_min/2, "Fecha", col = "#dc3545", cex = 0.7, font = 3, adj = 0)

# Pontos criticos
points(cme_min_q, cme_min, pch = 19, col = "#0d6efd", cex = 1.3)
text(cme_min_q, cme_min, paste0("  Break-even\n  CMe_min=", round(cme_min, 1)),
     pos = 4, cex = 0.7, col = "#0d6efd")

legend("topright",
       legend = c("CMg (= oferta acima CVMe)", "CMe", "CVMe"),
       col = c("#dc3545", "#0d6efd", "#198754"),
       lwd = c(3, 2, 2), lty = c(1, 1, 2), cex = 0.75, bg = "white")

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