code: function(sbm, n) {
      if (n == 0) {
        return this.identity(n)
      } else if (n == 1) {
        return sbm
      } else if (n % 2 == 0) {
        return this.pow(this.multiply(sbm, sbm), n/2)
      } else {
        return this.multiply(sbm, this.pow(this.multiply(sbm, sbm), (n-1)/2))
      }
    }
docs: power of the matrix