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The people on the perimeter are all 10 years old

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The people on the perimeter are all 10 years old. Inside the lattice, the age of each person is 3 more than the average of the four immediate neighbors (left, right, front, back). What would be a program to set up and solve a sparse system of equations for the ages of the 4 × 10 people inside the lattice. Print out these ages in the form of a table, with one decimal point of precision for each age.Note, a sparse system involves a matrix with many zeros in it. We'll find that often we have large matrices with many elements equal to zero. Matlab has the ability to ID matrices as sparse which helps with memory management.
PS: This question is complete, and doesn't have any more data. This is what my instructor hinted about the problem: " You are on the right track by unwrapping the 12x6 lattice into a 72x1 vector. You don't need to create the vector explicitly. Your goal is to solve for it from Ax = b.
You can find matrix A and vector b by writing down a equation that relates the age of a person inside the lattice with its neighbors. It would be similar to the equation for the 1D problem. Make sure you understand how matrix A is formed for the 1D problem, in other words where each one of the non-zero entries come from. (It's actually simply matrix multiplication.) Once you get that you will be able to form the matrix A for the 2D problem."
I'm still not sure how to solve this homework problem