User-Defined Functions

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• Misc
  • Rochester Math Olympiad
    • Western NY regional math problem-solving contest
    • 4 problems in 3 hours
    • Small cash prizes for top 3 finishers in region
    • Feb. 6 (this Saturday), 9:30 - 12:30
    • See Prof. Towsley to join
• Questions?
  • Turn in lab as Matlab .m script files
• Functions and Algorithms
  • Algorithm video
    • Algorithm = procedure (i.e., series of steps) for solving problem
    • Steps have to be definite (clear what they mean) and effective (doable)
    • Output must be finite (in time) and correct
      
  • Section 4.3
    • Function similar to an algorithm
    • Store with name you want
    • Statements in function get run by writing name
    • Functions have inputs, outputs
    • Using a function is “call”
    • Local variables exist only inside function
    • Function definition
      

      function output = name( input1, input2, …  )
          statements
      end

  • Example
    • Function that takes argument n and returns the average of n and 2n
      

      function [ avg ] = average( n )
      % average computes the average of n and 2n
      
      % Algorithm: add n + 2n
      %           divide by 2
      
      avg = ( n + 2*n ) / 2;
      
      end

    • Some calls on it:
      

      >> average( 2 )
      ans =
           3
      >> average(1)
      ans =
          1.5000
      >> average(117)
      ans =
        175.5000

• Next
  • Introduction to vectors
  • Read sections 5.1 - 5.6

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