Cell Arrays

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• Misc
  • Colloquium
    • Friday, Nov. 21 (today!) 2:30, Newton 204
    • “Mathematical Modeling of Cardiac Arrhythmias”
    • Dr. Elizabeth Cherry, RIT
    • Extra credit for attending and writing summary/reaction (email is fine)
• Questions?
• Cell Arrays
  • Section 8.1
    • Store different types of value, unlike matrices
    • Curly brackets
    • Content vs cell indexing
      
    • Cell array functions
      • celldisp
      • cellplot
  • Why?
    • Suppose you want to record a list of numbers and why each is “interesting”
    • Obvious approach with what we know so far is to make one vector of numbers and another of reasons
      

      >> numbers(1) = 2;
      >> reasons(1) = 'even prime';
      {Subscripted assignment dimension mismatch.
      } 
      >> reasons(1,:) = 'even prime';
      >> reasons
      reasons =
      even prime
      >> numbers(2) = 1;
      >> reasons(2,:) = 'multiplicative identity'
      {Subscripted assignment dimension mismatch.
      } 
      >> size( reasons )
      ans =
           1    10

    • Main problem is that strings are vectors of characters, and different strings are different length vectors
    • Cell arrays avoid this incompatibility of lengths, and of types that forced us to keep the numbers and reasons in separate vectors in the first place
      

      >> clear
      >> numbers = { 2, 'even prime' }
      numbers = 
          [2]    'even prime'
      >> % second row of numbers gets { 1, 'mult. id.' }
      >> numbers(2,:) = { 1, 'multiplicative identity' }
      numbers = 
          [2]    'even prime'          
          [1]    'multiplicative id...'
      >> numbers{1,2}
      ans =
      even prime
      >> numbers(1,2)
      ans = 
          'even prime'
      >> class( numbers(1,2) )
      ans =
      cell
      >> class( numbers{1,2} )
      ans =
      char

• Files and Variables
  • Once you can build big complex data structures via cell arrays, you’re likely to want to save them beyond a single Matlab session—i.e., in files
  • save and load commands do this
    

    >> save NumberInfo numbers
    >> clear
    >> clc
    >> load NumberInfo
    >> numbers
    numbers = 
        [2]    'even prime'         
        [1]    'multiplicative i...'

• Relations Lab
  • Handout
  • Relation = ...?
    • e.g., relation between x and y such that x² + y² = 0
      • Holds of x=0, y=0
      • Doesn’t hold for x=1, y=7
    • Other examples: less than, equal to, etc.
  • Definition: set of ordered pairs
    • e.g., x²+y² = 0 is { (0,0) }
    • < is infinite set { ..., (-1,0), (-1,1), (0,1), (17, 984), ... }
• Next
  • More on relations
  • Start planning and coding lab

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