title: Multiplying upper triangular matrix stored in 1D array alogrithm
body: <p>I am doing the upper triangular matrix multiplication in c++. Those matrices are stored in 1D array instead of normal 2D arrays. The value are stored inside the array from row to row and the 0's at the bottom part are ignored. I did a lot of mathematics, trying to find out a pattern, but I still cannot think of an algorithm. Suppose I have 2 matrices and each one is in the square shape and both of those values are stored in the 1D array A and B. And I want to store the results in an array C. I think The hardest part is adding varying number of changing elements as the for loop runs.</p>
  
  <p>Anyone could give me some inspirations? </p>