Overview

• Admin.
• QUIZ!
• Random art.
• Why use randomness.
• The random procedure.
• Simulation.

Admin

• There will be time for questions on assignment 8, which is our last assignment.
• There's been a request that I talk about vector-fill!
• Next Friday we will be moving our class to the 3rd floor ARH lecture hall (302, I believe) to hear Hilary Mason '00. Class starts at 12:45.
  • So no quiz next week
• Upcoming extra credit opportunities:
  • 6pm event in Main Quad
  • A love-your-body week event.
  • Drag show. (Yes, this is in addition to the other lyb events.)
  • Basketball, Saturday, 3pm, Alumni
  • Concert, Saturday, 7:30, S-L.
  • Post-24-hour show, Saturday, 7:30, ???
  • Town Hall, Wednesday, November 13, noon or 7:30 p.m.
  • Learning from Alumni, Thursday: Atul Gupta, Trustee, 2:15-4:05
  • CS Extra, Thursday: Hilary Mason '00
  • CS Table, Next Friday, HCI
  • CLS with Hilary Mason '00, Friday, ???
  • Football, noon, a week from tomorrow
  • Digital Commons talk Monday, November 19, 7:00 p.m. or so

Question on Vector-Fill!

; Goal of vector-fill!: Fill an existing vector with a particular value
> (define v (vector 1 2 3))
> v
'#(1 2 3)
> (vector-fill! v 0)
> v
'#(0 0 0)

; An INCORRECT solution
(define vector-fill!
  (lambda (vec val)
    (make-vector (vector-length vec) val)))
; This does not achieve the required goals.  Yes, it gives a vector
; of the required form, but it's a NEW vector.  (It doesn't mutate.)

(define vector-phil!
  (lambda (vec val)
    (for-each (lambda (i) (vector-set! vec i val))
              (iota (vector-length vec)))))

(define vector-pfil!
  (lambda (vec val)
    (let kernel ([pos 0])
      (when (< pos (vector-length vec))
        (vector-set! vec pos val)
        (kernel (+ pos 1))))))

Does it make a difference if you iteratire from vector-length to 0 or from 0 to vector-length?

Not really, it depends on the problem. Try one, see how well it works.

Questions on Homework

Random art

Why use randomness

The procedure

Simulation