Slight changes to trade constraints.

src/ac/ed/lurg/country/CountryAgent.java

@@ -178,7 +178,7 @@ public class CountryAgent extends AbstractCountryAgent {
 
 				if (crop.isImportedCrop()) {
 					changeUp = cropPrice.getTradeChangeUp(maxOfProdOrSupply);
-					changeDown = cropPrice.getTradeChangeDown(maxOfProdOrSupply, crop.getStockToUseRatio());
+					//changeDown = cropPrice.getTradeChangeDown(maxOfProdOrSupply, crop.getStockToUseRatio());
 
 					if (changeUp < 0) { // need to reduce imports to avoid negative stocks
 						baseTrade += changeUp;
@@ -225,7 +225,7 @@ public class CountryAgent extends AbstractCountryAgent {
 			} else {
 				double maxOfProdOrSupply = carbonUsageData.getCarbonCredits() + Math.max(baseTrade, 0);
 				changeUp = globalCarbonPrice.getTradeChangeUp(maxOfProdOrSupply);
-				changeDown = globalCarbonPrice.getTradeChangeDown(maxOfProdOrSupply, ModelConfig.DEFAULT_STOCK_USE_RATIO);
+				changeDown = maxOfProdOrSupply * ModelConfig.MAX_IMPORT_CHANGE;
 
 				if (changeUp < 0) { // need to reduce imports to avoid negative stocks
 					baseTrade += changeUp;
@@ -260,7 +260,7 @@ public class CountryAgent extends AbstractCountryAgent {
 				changeUp = changeDown = 0.0;
 			} else {
 				changeUp = woodPrice.getTradeChangeUp(maxOfProdOrSupply);
-				changeDown = woodPrice.getTradeChangeDown(maxOfProdOrSupply, ModelConfig.DEFAULT_STOCK_USE_RATIO);
+				changeDown = maxOfProdOrSupply * ModelConfig.MAX_IMPORT_CHANGE;
 
 				if (changeUp < 0) { // need to reduce imports to avoid negative stocks
 					baseTrade += changeUp;
@@ -290,7 +290,7 @@ public class CountryAgent extends AbstractCountryAgent {
 		double prodCost = cropUsageData.getProdCostRate();
 		Double tb = tradeBarriers.get(crop);
 		double tradeBarrier = tb==null ? 0 : tb;
-		double exportTaxRateForCrop = CommodityType.CEREALS.getCropTypes().contains(crop) ? exportTaxRate : 0.0;
+		double exportTaxRateForCrop = CommodityType.CEREALS_STARCHY_ROOTS.getCropTypes().contains(crop) ? exportTaxRate : 0.0;
 		CountryPrice cp = new CountryPrice(crop, worldPrice, tradeBarrier, prodCost, weighting, exportTaxRateForCrop);
 		return cp;
 	}

src/ac/ed/lurg/country/GlobalPrice.java

@@ -119,8 +119,9 @@ public class GlobalPrice implements Serializable {
 				// Adjust price based on stock change
 				adjustment = 1 - lambda * stockChange / production;
 
-				// If below target stock and stocks not already increasing, nudge prices to increase stock.
-				if (updatedStock < targetStock & stockChange < 0) {
+				// If below target stock and stocks not already increasing, nudge prices up to increase stock.
+				// If above target stock and stocks not already decreasing, nudge prices down to decrease stock.
+				if ((updatedStock < targetStock & stockChange < 0 & stockChange < prevStockChange) | (updatedStock > targetStock & stockChange > 0 & stockChange > prevStockChange)) {
 					adjustment *= 1 - 0.5 * ModelConfig.MARKET_LAMBDA * (updatedStock - targetStock) / production;
 				}
 			}
@@ -195,15 +196,7 @@ public class GlobalPrice implements Serializable {
 		maxOfProdOrSupply += 0.05 * production / CountryManager.getInstance().getCountryCount();
 		double supplyFraction = maxOfProdOrSupply / (production * 1.05);
 		// ensures stocks don't go below zero even if no exports
-		return (0.95 * stockLevel - (importAmount - getExportsAfterTransportLosses())) * supplyFraction;
-	}
-
-	public double getTradeChangeDown(double maxOfProdOrSupply, double targetStockUseRatio) {
-		// plus 5% of global production divided by number of countries in case country has 0 supply
-		maxOfProdOrSupply += 0.05 * production / CountryManager.getInstance().getCountryCount();
-		double supplyFraction = maxOfProdOrSupply / (production * 1.05);
-		// Allow exports to increase until stocks 50% above target stock level
-		return Math.max(targetStockUseRatio * production * 1.5 - stockLevel, 0) * supplyFraction;
+		return (0.9 * stockLevel - (importAmount - getExportsAfterTransportLosses())) * supplyFraction;
 	}
 
 }
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