title: what is RHS vector
body: <p>please I am trying to understand matrix computation. 
  and my question may seem simple but please need an answer
  can some briefly explain to me what is an RHS vector.
  I often see it used in the Apache commons math library
   for example i got this from a stackoverflow page:  </p>
  
  <pre><code>public class LinearAlgebraDemo
  {
      public static void main(String[] args)
      {
          double [][] values = {{1, 1, 2}, {2, 4, -3}, {3, 6, -5}};
          double [] rhs = { 9, 1, 0 }; /* RHS Vector */
  
          RealMatrix a = new Array2DRowRealMatrix(values);
  
          DecompositionSolver solver = new LUDecompositionImpl(a).getSolver();
  
          RealVector b = new ArrayRealVector(rhs);
          RealVector x = solver.solve(b);
  
          RealVector residual = a.operate(x).subtract(b);
          double rnorm = residual.getLInfNorm();
  
      }
  }
  </code></pre>
  
  <p>can someone explain this code to me and especially the RHS vector and its purpose.
  thank you very much.</p>