k is number of segments, i means firm i, and t shows the period, let's say we have Microsoft and k for microsoft is 4, there are sales data for micorsoft for each segment for 3 periods and this is how the series look like: (Sales)(k=1)(t=1)*ln(1/sales), so the sum is the sum of sales*ln(1/sales) for each firm , for each period and for each segment.
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