### Question:
EyePlusLaplacianMatrix extends AbstractMatrix implements SymMatrix { @Override public void mult(Vector x, Vector y) { if (x instanceof DenseDoubleVector && y instanceof DenseDoubleVector) { DenseDoubleVector xx = (DenseDoubleVector) x; DenseDoubleVector yy = (DenseDoubleVector) y; mult(xx.data, yy.data); } else { throw new MatricksException("Not implemented"); } } EyePlusLaplacianMatrix(SymMatrix backing); @Override int numRows(); @Override int numCols(); @Override double get(int row, int col); @Override void set(int row, int col, double val); @Override MatrixCursor cursor(); @Override void multAdd(double alpha, Vector x, Vector y); @Override void mult(Vector x, Vector y); @Override // todo: update to use vector ops void multAdd(double alpha, double[] x, double[] y); @Override // todo: update to use vector ops void mult(double[] x, double[] y); @Override SymMatrix subMatrix(int[] rowcols); @Override void setDiag(double alpha); @Override void addOuterProd(double[] x); @Override double sumDotMultOuterProd(double[] x);  }### Answer:
@Test public void testMult() throws Exception { FlexSymFloatMatrix c = new FlexSymFloatMatrix(4); c.set(0, 1, 0.88715); c.set(0, 2, 0.67974); c.set(0, 3, 0.69090); c.set(1, 2, 0.99739); c.set(1, 3, 0.70729); c.set(2, 3, 0.97997); DenseDoubleVector ones = new DenseDoubleVector(4); ones.set(0, 1); ones.set(1, 1); ones.set(2, 1); ones.set(3, 1); EyePlusLaplacianMatrix m = new EyePlusLaplacianMatrix(c); DenseDoubleVector result = new DenseDoubleVector(4); m.mult(ones, result); assertEquals(1.0, result.get(0), 1e-4); assertEquals(1.0, result.get(1), 1e-4); assertEquals(1.0, result.get(2), 1e-4); assertEquals(1.0, result.get(3), 1e-4); }