Matrix Share mode is only available if an existing matrix is active and therefore, it is not available in Summary view.
Matrix Share mode takes your existing matrix and displays the data as a percentage, with each row summing to 100 per cent. It is a useful tool where ratios are important, for example, if you want to compare the ratio of Product X to Product Y.
The following example uses Matrix Share mode to identify which customers have bought downlights but not transformers, both this year and last year. Suppose you know that typically one transformer is required to run two downlights. That is, a 33.3% / 66.6% split, based on quantity. You want to identify the customers that are outside that ratio, in other words, which customers are buying fewer transformers than expected.
Start with an existing a matrix (this example continues with the example in the Compare data with Matrix mode page).
Select Measures > Quantity and remove the Local Value measure.
Select Mode > Matrix Share. The grid updates to display the quantity data rather than the local values, and the percentage split for each customer, for each item (the columns sum to 100%).
(Optional) Go back to your regular matrix: click Mode > Matrix.