Problem 1100. Design matrix from eigenvalues

Write a function that takes one input argument n and outputs a (n x n) square matrix A with the following properties:

 -A has an eigenvalue of 3

 -all elements of A differ more than .5 from each other.

   For example

A=matrix_design(3)

A=

     4    -3     2
    -1     1     3
     0     5    -2