code: public DoubleMatrix1D solve(DoubleMatrix1D b) {
  		if (b.size() != dim) {
  			log.error("wrong dimension of vector b: expected " + dim + ", actual "	+ b.size());
  			throw new RuntimeException("wrong dimension of vector b: expected " + dim	+ ", actual " + b.size());
  		}
  
  		throw new RuntimeException("not yet implemented");
  	}
docs: Solves Q.x = b
  @param b vector
  @return the solution x
  @see "S.Boyd and L.Vandenberghe, Convex Optimization, p. 672"
  @TODO: implement this method