A simple function to add vectors. Zero pads vectors to the length of the longest

vec+.clj

(defn vec+
  ([] nil)
  ([v1] v1)
  ([v1 v2]
     (let [c1 (count v1)
           c2 (count v2)
           seq (if (< c1 c2)
                 (map + (concat v1 (repeat 0)) v2)
                 (map + (concat v2 (repeat 0)) v1))]
       (vec seq)))
  ([ v1 v2 & vn]
     (reduce vec+ (vec+ v1 v2) vn)))