code: @Override
      public void solve(DMatrixRMaj B , DMatrixRMaj X ) {
          if( B.numRows != n ) {
              throw new IllegalArgumentException("Unexpected matrix size");
          }
          X.reshape(n,B.numCols);
  
          if(decomposer.isLower()) {
              solveLower(A,B,X,vv);
          } else {
              throw new RuntimeException("Implement");
          }
      }
docs: <p>
  Using the decomposition, finds the value of 'X' in the linear equation below:<br>
  
  A*x = b<br>
  
  where A has dimension of n by n, x and b are n by m dimension.
  </p>
  <p>
  *Note* that 'b' and 'x' can be the same matrix instance.
  </p>
  
  @param B A matrix that is n by m.  Not modified.
  @param X An n by m matrix where the solution is writen to.  Modified.