Implement restrictions to the decision to sell one's home

These new restrictions include:
- Do not sell if maximum mortgage price limit would bring the household to rent anyway
- Do not sell if a cash purchase would not lead to an increase in quality

src/main/java/housing/Household.java

@@ -429,7 +429,7 @@ private void bidForAHome() {
  ********************************************************/
  private boolean decideToSellHouse(House h) {
  if(h == home) {
- return(behaviour.decideToSellHome());
+ return(behaviour.decideToSellHome(this, h));
  } else {
  return(behaviour.decideToSellInvestmentProperty(h, this));
  }

src/main/java/housing/HouseholdBehaviour.java

@@ -170,13 +170,30 @@ public class HouseholdBehaviour {
 
  /**
  * This method implements a household's decision to sell their owner-occupied property. On average, households sell
- * owner-occupied houses every 11 years, due to exogenous reasons not addressed in the model.
- *
- * @return True if the owner-occupier decides to sell the house and false otherwise.
+ * owner-occupied houses every X years, due to exogenous reasons not addressed in the model.
+ * @param me the household considering selling
+ * @param h the house that might be put for sale
+ * @return True if the owner-occupier decides to sell the house, false otherwise
  */
- boolean decideToSellHome() {
- // TODO: This if implies BTL agents never sell their homes, need to explain in paper!
- return !isPropertyInvestor() && (prng.nextDouble() < config.derivedParams.MONTHLY_P_SELL);
+ boolean decideToSellHome(Household me, House h) {
+ // Quick decisions...
+ // ...households with the BTL flag never sell their homes
+ if (isPropertyInvestor()) {
+ return false;
+ }
+ // ...do not consider selling if maximum mortgage price constraint would make the household choose renting
+ if ((me.getDesiredPurchasePrice() > Model.bank.getMaxMortgagePrice(me, true)) && (me.getAge() > 35.0)) {
+ return false;
+ }
+ // ...do not consider selling if the household's current net wealth would not allow it to move up in quality
+ double netWealth = me.getBankBalance() + housingMarketStats.getExpAvSalePriceForQuality(h.getQuality())
+ - ((MortgageAgreement) me.getHousePayments().get(h)).principal;
+ if ((housingMarketStats.getMaxQualityForPrice(netWealth) <= h.getQuality()) && (me.getAge() > 45.0)) {
+ return false;
+ }
+
+ // Finally, if none of the above kicks in, apply the calibrated monthly probability to sell
+ return prng.nextDouble() < config.derivedParams.MONTHLY_P_SELL;
  }
 
  /**