3 arrays is directly equivalent to an array of 2 arrays or an array of tuples of index,value. As for how it's efficient, that's obvious: column eg 3 will be an

3 arrays is directly equivalent to an array of 2 arrays or an array of tuples of index,value. As for how it's efficient, that's obvious: column eg 3 will be an array of tuples like [(1,3), (11,17), (9936,3)] so there are nz values in locations [1, 3] = 3 [11, 3] = 17 [9936, 3] = 3 so csc makes it efficient to read down columns, ie right multiply by the transpose. My implementation makes it easier to update in the sense of inserting values at indices where previously the value was empty, since you only have to reorder a single column instead of all following data from top to bottom then left to right. Once finished inserting values, if ever, you may want to move to two packed arrays. What makes me shake my head is you don't understand what csc matrices are but didn't let that stop you from telling me I don't understand them. HN in a nutshell.