Program: 57487
Project: 57487
Buggy source:
/** 
 * {@inheritDoc} 
 */
public RealMatrix solve(RealMatrix b) throws IllegalStateException, IllegalArgumentException, InvalidMatrixException {
  final int n=qrt.length;
  final int m=qrt[0].length;
  if (b.getRowDimension() != m) {
    throw new IllegalArgumentException("String_Node_Str");
  }
  if (!isNonSingular()) {
    throw new SingularMatrixException();
  }
  final int cols=b.getColumnDimension();
  final double[][] xData=new double[n][cols];
  final double[] y=new double[b.getRowDimension()];
  for (int k=0; k < cols; ++k) {
    for (int j=0; j < y.length; ++j) {
      y[j]=b.getEntry(j,k);
    }
    for (int minor=0; minor < Math.min(m,n); minor++) {
      final double[] qrtMinor=qrt[minor];
      double dotProduct=0;
      for (int row=minor; row < m; row++) {
        dotProduct+=y[row] * qrtMinor[row];
      }
      dotProduct/=rDiag[minor] * qrtMinor[minor];
      for (int row=minor; row < m; row++) {
        y[row]+=dotProduct * qrtMinor[row];
      }
    }
    for (int row=n - 1; row >= 0; --row) {
      y[row]/=rDiag[row];
      final double yRow=y[row];
      final double[] qrtRow=qrt[row];
      xData[row][k]=yRow;
      for (int i=0; i < row; i++) {
        y[i]-=yRow * qrtRow[i];
      }
    }
  }
  return new RealMatrixImpl(xData,false);
}

Fixed version (ground truth):
/** 
 * {@inheritDoc} 
 */
public RealMatrix solve(RealMatrix b) throws IllegalArgumentException, InvalidMatrixException {
  final int n=qrt.length;
  final int m=qrt[0].length;
  if (b.getRowDimension() != m) {
    throw MathRuntimeException.createIllegalArgumentException("String_Node_Str",new Object[]{b.getRowDimension(),b.getColumnDimension(),m,"String_Node_Str"});
  }
  if (!isNonSingular()) {
    throw new SingularMatrixException();
  }
  final int columns=b.getColumnDimension();
  final int blockSize=DenseRealMatrix.BLOCK_SIZE;
  final int cBlocks=(columns + blockSize - 1) / blockSize;
  final double[][] xBlocks=DenseRealMatrix.createBlocksLayout(n,columns);
  final double[][] y=new double[b.getRowDimension()][blockSize];
  final double[] alpha=new double[blockSize];
  for (int kBlock=0; kBlock < cBlocks; ++kBlock) {
    final int kStart=kBlock * blockSize;
    final int kEnd=Math.min(kStart + blockSize,columns);
    final int kWidth=kEnd - kStart;
    b.copySubMatrix(0,m - 1,kStart,kEnd - 1,y);
    for (int minor=0; minor < Math.min(m,n); minor++) {
      final double[] qrtMinor=qrt[minor];
      final double factor=1.0 / (rDiag[minor] * qrtMinor[minor]);
      Arrays.fill(alpha,0,kWidth,0.0);
      for (int row=minor; row < m; ++row) {
        final double d=qrtMinor[row];
        final double[] yRow=y[row];
        for (int k=0; k < kWidth; ++k) {
          alpha[k]+=d * yRow[k];
        }
      }
      for (int k=0; k < kWidth; ++k) {
        alpha[k]*=factor;
      }
      for (int row=minor; row < m; ++row) {
        final double d=qrtMinor[row];
        final double[] yRow=y[row];
        for (int k=0; k < kWidth; ++k) {
          yRow[k]+=alpha[k] * d;
        }
      }
    }
    for (int j=rDiag.length - 1; j >= 0; --j) {
      final int jBlock=j / blockSize;
      final int jStart=jBlock * blockSize;
      final double factor=1.0 / rDiag[j];
      final double[] yJ=y[j];
      final double[] xBlock=xBlocks[jBlock * cBlocks + kBlock];
      for (int k=0, index=(j - jStart) * kWidth; k < kWidth; ++k, ++index) {
        yJ[k]*=factor;
        xBlock[index]=yJ[k];
      }
      final double[] qrtJ=qrt[j];
      for (int i=0; i < j; ++i) {
        final double rIJ=qrtJ[i];
        final double[] yI=y[i];
        for (int k=0; k < kWidth; ++k) {
          yI[k]-=yJ[k] * rIJ;
        }
      }
    }
  }
  return new DenseRealMatrix(n,columns,xBlocks,false);
}