tomography-reconstruction

I am trying to use MATLAB to implement a CT (computed tomography) projection operator, A, which I think is also referred as "system matrix" often times. Basically, for a N x N image M, the projection data, P, can be obtained by multiplication of the project operator to the image: P = AM and the backprojection procedure can be performed by multiplying the (conjugate) transpose of the projection operator to the projection data: M = A'P Anyone has any idea/example/sample code on how to implement matrix A (for example: Radon transform)? I would really like to start with a small size of matrix, say

How to find out if it is possible to contruct a binary matrix with given row and column sums. Input : The first row of input contains two numbers 1≤m,n≤1000, the number of rows and columns of the matrix. The next row contains m numbers 0≤ri≤n – the sum of each row in the matrix. The third row contains n numbers 0≤cj≤m – the sum of each column in the matrix. Output: Output “YES” if there exists an m-by-n matrix A, with each element either being 0 or 1. Else "NO". I tried reading about Tomography algorithms but could not figure out an answer as all the papers related to Tomography algorithm is