Lecture 9: Problem Session and Quiz

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Assignments

These are the problems you should work before today, February 5.
Review problems, page 75, 4n+1, for n=0..22;
Section 1.1, page 92, 4n+1, for n=0...24;
Section 1.2, page 102, 1-6, and 4n, for n=3...23;
Section 1.3, page 113, 4n+1, for n=0...19.

These are the problems you should work before February 12.
Section 1.4, page 120, problems 6n+1, for n=0...15;
(skip 1.5) 1.6, page 149, problems 6n+1, for n=0...16.

These are the problems you should work before February 19.
Section 1.7, page 160, 4n+1, for n=0,...,24.
Section 1.8, page 171, problems 6n+1, for n=0...8;

These are the problems you should work before February 26.
The first test, covering Chapters P and 1 and sections 2.1 and 2.2 is on February 26.
Section 2.1, page 191, problems 6n+1, for n=0...12.
Section 2.2, page 025, problems 8n+1, for n=0...11.

Brief review of the lecture

As usual, this material is left from last semester. You may safely disregard it. The material covered today does not appear anywhere in the text. If you missed this lecture, you must get the notes from a classmate.

An assignment statement gives a value to a variable. " x:=4 " is an example. Another example is " x:=x-1 ". We attempt here to give a 'mathematical' meaning to these statements. To do this we construct a function for each statement which describes the value of the variable(s) after the statements execution in terms of the value(s) before. In the first case we get the constant function f(x)=4, and in the second, we get f(x)=x-1.

  • An example of an IF-THEN_ELSE statement is " if x < 2 then x:=x+1 else x:=2 ".

  • Several IF-THEN-ELSE statements can be combined.

    Let f(x) be defined by the following statement :

    If x<=3 the x:=x-3 else x:=2x+4

    and g(x) be defined by the statement :

    If x>2 then x:=x+1 else x:=2x-1.

    Then we may combine the two statements together, starting with f(x), to obtain g(f(x)) =

  • (x-3)+1 if x<=3 and x-3>2
  • 2(x-3)-1 if x<=3 and x-3<=2
  • (2x+4)+1 if x>3 and 2x+4>2
  • 2(2x+4)-1 if x>3 and 2x+4<=2


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