title: How to Update values of a sparse matrix in Armadillo
body: <p>I am solving a Fluid Problem in which very large Sparse Matrix forms. In the context of Armadillo Sparse Matrix, I have a fixed <code>umat locations</code> matrix of storing indices and a variable <code>vec values</code> for each location. I have created a Sparse Matrix with Armadillo as <code>sp_mat A(locations, values)</code> before iteration starts. In each iteration I need solve for different <code>values</code>, <code>locations</code> remains same, and I wish update values in <code>A</code>.</p>
  
  <p>Is there any way by which I can update <code>values</code> in <code>A</code>, replacing older ones with <code>batch insertion</code>, or any similar, methods provided in Armadillo? If no, then what is the best method, in the context of Speed, to do so?</p>
  
  <p>Element Access, <code>A(i,j)</code>, is possible but due to large size it slow down the process. Batch Insertion seems faster and manageable.</p>
  
  <p>Thanks a LOT !! </p>