Class 31: Numeric Recursion

Held:

Preliminaries

Related Pages

• Eboard 31 (Source)

• Reading: Numeric Recursion

• Lab: Numeric Recursion

Updates

News / Etc.

• New partners!

Rotating reminders

• Visit review sessions! I run review sessions on Thursdays at 9am in this room.
• Visit mentor sessions! We have mentor sessions on Thursday evening from 8:00-9:00 p.m. in the CS Commons.

Upcoming Work

• Lab writeup: Execise 3
• Reading for Friday: Naming Local Procedures
• No homework over break.
• Friday’s quiz: Identify your classmates

Extra credit (Academic/Artistic)

Extra credit (Peer)

• Singers Concerts during spring break.
  • If there is an admission fee, I will reimburse up to $20.
• Baseball games during spring break (Arkansas & Alabama).
  • If there is an admission fee, I will reimburse up to $20.
• Baseball games last weekend of spring break. (1 hour suffices; no more than two units for the weekend.)

Extra credit (Misc)

Good things to do

• Ultimate games during spring break.

Patterns of Recursion

While we’ve seen and written a variety of examples of direct recursion, they typically have the following form:

(define RECURSIVE-PROC
  (lambda (PARAMS)
    (if (BASE-CASE-TEST)
        (BASE-CASE PARAMS)
        (COMBINE (PART-OF PARAMS)
                 (RECURSIVE-PROC (SIMPLIFY PARAMS))))))

For lists, the simplification was almost always “take the cdr” and the “part-of” was almost always “take the car”.

Recursion with Numbers

• While most of the recursion we’ve been doing has used lists as the structure to recurse over, you can recurse with many different kinds of values.
• It is fairly common to recurse using numbers.
• The natural base cases for integers are when you hit 0 or when you hit 1.
• The natural simplification step for recursive procedure using numbers calls typically involves subtracting 1 from the argument.
  • Other simplifications, such as dividing in half, are also possible.

Lab

• Do the lab