matrix.clj

(def mat [[1 2 3 4 5]
          [6 7 8 9 10]
          [11 12 13 14 15]
          [16 17 18 19 20]])

(defn walk-matrix
  "Walks along the rows and columns of a matrix at the given window
  size, returning all (window x window) snapshots."
  [matrix window]
  (letfn [(walk-rows [rows]
                     (apply map vector
                            (map #(partition window 1 (matrix %))
                                 rows)))]
    (reduce conj (map (comp vec walk-rows)
                      (partition window 1 (range (count matrix)))))))