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PODynamic programming with large inputs
 

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  1. PODynamic programming with large inputs
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    <p>I am trying to solve a classic Knapsack problem with huge capacity of 30.000.000 and it works well up until 20.000.000 but then it runs out of memory:</p> <pre> Exception in thread "main" java.lang.OutOfMemoryError: Java heap space </pre> <p>I have tried to divide all values and capacity by 1.000.000 but that generates floats and I don't think that is the correct approach. I have also tried to make the arrays and matrix of type long but that does not help. Perhaps another data-structure? Any pointers welcome...</p> <p>Code: <pre> public class Knapsack { public static void main(String[] args) { int N = Integer.parseInt(args[0]); // number of items int W = Integer.parseInt(args[1]); // maximum weight of knapsack</p> <code> int[] profit = new int[N+1]; int[] weight = new int[N+1]; // generate random instance, items 1..N for (int n = 1; n &lt;= N; n++) { profit[n] = (int) (Math.random() * 1000000); weight[n] = (int) (Math.random() * W); } // opt[n][w] = max profit of packing items 1..n with weight limit w // sol[n][w] = does opt solution to pack items 1..n with weight limit w include item n? int[][] opt = new int[N+1][W+1]; boolean[][] sol = new boolean[N+1][W+1]; for (int n = 1; n &lt;= N; n++) { for (int w = 1; w &lt;= W; w++) { // don't take item n int option1 = opt[n-1][w]; // take item n int option2 = Integer.MIN_VALUE; if (weight[n] &lt;= w) option2 = profit[n] + opt[n-1][w-weight[n]]; // select better of two options opt[n][w] = Math.max(option1, option2); sol[n][w] = (option2 &gt; option1); } } // determine which items to take boolean[] take = new boolean[N+1]; for (int n = N, w = W; n &gt; 0; n--) { if (sol[n][w]) { take[n] = true; w = w - weight[n]; } else { take[n] = false; } } // print results System.out.println("item" + "\t" + "profit" + "\t" + "weight" + "\t" + "take"); for (int n = 1; n &lt;= N; n++) { System.out.println(n + "\t" + profit[n] + "\t" + weight[n] + "\t" + take[n]); } //Copyright © 2000–2011, Robert Sedgewick and Kevin Wayne. Last updated: Wed Feb 9 //09:20:16 EST 2011. } </code></pre>
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    1. COHave you tried increasing the heap size with -X:MaxPermGen=512m?
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      1. USChris Chambers
    2. CO@ChrisChambers Considering error message it's not lack of PermGen space. If increasing anything then use -Xmx option, like for example -Xmx2048m
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    3. COAs suggested by Keyser, you only need the value of opt[n-1][] to calculate opt[n]. Hence you can do with a 1D array and overwrite it.
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      1. USAbhishek Bansal
 

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