Question

I am using jama libarary for matrix. I used following matrix but when i tried to get S, it gave me error.

1.0    1.0    0.0    1.0    0.0    0.0    0.0    0.0    0.0   11.0    1.0
1.0    0.0    0.0    0.0    0.0    0.0    1.0    0.0    0.0   12.0    2.0
1.0    1.0    0.0    0.0    0.0    0.0    0.0    0.0    1.0   13.0    3.0

When I tried to get S it produce following error.

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
    at Jama.SingularValueDecomposition.getS(SingularValueDecomposition.java:507)
    at SVD2.main(SVD2.java:19)

Here is the code

public class SVD2 {
    public static void main(String[] args) {
        double[][] vals = {
              {1,1,0,1,0,0,0,0,0,11,1},
              {1,0,0,0,0,0,1,0,0,12,2},
              {1,1,0,0,0,0,0,0,1,13,3}
              };
        Matrix A = new Matrix(vals,3,11);
        System.out.println("The Matrix A is ");
        A.print(11, 2);
        System.out.println();

        System.out.println("The SVD of A is ");
        SingularValueDecomposition svd = A.svd();
        Matrix S = svd.getS();       
    }

}

Answer 1

For Jama’s singular value decomposition, the number of rows must not be less than the number of columns. Maybe you should try SVD on the transpose of the matrix you provided.

EDIT: Here’s the relevant code from SingularValueDecomposition.java:

   public Matrix getS () {
      Matrix X = new Matrix(n,n);
      double[][] S = X.getArray();
      for (int i = 0; i < n; i++) {
         for (int j = 0; j < n; j++) {
            S[i][j] = 0.0;
         }
         S[i][i] = this.s[i];
      }
      return X;
   }

S is constructed to be an n x n array, so the only possible source of an ArrayIndexOutOfBoundsException is from the reference to this.s[i].

Space for s is initialized in the SingularValueDecomposition constructor (amd no where else) like this:

s = new double [Math.min(m+1,n)];

So the Jama implementation will work for a 2×3 input (contradicting what they say in the class javadoc). But I bet it won’t work for a 2×4 input.