### Question:
FlexSymDoubleMatrix extends AbstractMatrix implements SymMatrix { public void multAdd(final double alpha, Vector x, Vector y) { if (x instanceof DenseDoubleVector && y instanceof DenseDoubleVector) { DenseDoubleVector xx = (DenseDoubleVector) x; DenseDoubleVector yy = (DenseDoubleVector) y; multAdd(alpha, xx, yy); } else { throw new RuntimeException("not implemented"); } } FlexSymDoubleMatrix(int size); int numRows(); int numCols(); double get(int row, int col); void set(int row, int col, double val); void scale(final double a); void setAll(double a); MatrixCursor cursor(); void add(Matrix B); void add(final double a, Matrix B); void add(final double alpha, FlexSymDoubleMatrix B); double elementSum(); double elementMultiplySum(Matrix m); double elementMultiplySum(FlexSymDoubleMatrix m); void CG(Vector b, Vector x); boolean converged(int iter, double initR, double currentR, Vector x); void QR(Vector x, Vector y); Vector rowSums(); Vector columnSums(); void rowSums(double [] result); void columnSums(double [] result); void setToMaxTranspose(); void multAdd(final double alpha, Vector x, Vector y); void multAdd(final double alpha, DenseDoubleVector x, DenseDoubleVector y); void multAdd(final double alpha, double [] x, double [] y); void multAdd(double [] x, double [] y); void mult(Vector x, Vector y); void mult(DenseDoubleVector x, DenseDoubleVector y); void mult(double [] x, double [] y); void dotMultOuterProd(double [] x, double [] y); void dotDivOuterProd(double [] x, double [] y); void dotMultOuterProd(double [] x); void dotDivOuterProd(double [] x); void dotDivOuterProd(Vector x); void dotDivOuterProd(DenseDoubleVector x); void addOuterProd(double [] x); double sumDotMultOuterProd(double [] x); SymMatrix subMatrix(int [] rowcols); Matrix subMatrix(int [] rows, int [] cols); void setDiag(double alpha); void add(int i, int j, double alpha); void compact(); void transMult(double [] x, double [] y);  }### Answer:
@Test public void testMultAdd() throws MatricksException { int size = 5; FlexSymDoubleMatrix m = makeTestMatrix(size); double [] vec = makeTestVectorData(size); double [] result = new double[size]; m.multAdd(1d, vec, result); System.out.println("out: " + result); }