In MATLAB, ask the user to input a matrix of any size. Ensure that the user inputs a positive, integer matrix. If there is an incorrect input, ask them for a matrix again. Use Loops to do this.

Using loops, find the sum of all prime numbers present in the user-entered matrix. You must not use the built-in isprime function to do this. Use loops. (The number 1 may count as as a prime number)

Example Matrix: [1 2 3; 4 5 6; 7 8 9]