How to write angular distribution formula

I have to receive angular information from Radon transform. Formula for Radon transform:

From this formula I got the matrix of doubles R with dimensions(145;180) and an array s of a size=145. Now I need to get the angular distribution array a(180) which can be solved by the formula:

(RT means Radon Transform)

How can I write that on MATLAB?

[J. Alex Lee]

by "angular distribution" do you mean the probability density of angles represented in your original image?