While Loops

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• Misc
  • Colloquium
    • “ARE U Planning for Next Summer / Modeling Cardiovascular Dynamics During Blood Withdrawal”
    • REU programs and the work of one particular one
    • Jacob Goldberg, Geneseo Math major
    • Wednesday, Oct. 21, 2:45, Newton 204
    • Extra credit as usual (but connections need to be more than “I want to do an REU”)
  • First hour exam
    • Friday (Oct. 23)
    • Material from start of semester through matrices (e.g., arithmetic, scripts & functions, vectors, plotting, matrices, etc.)
    • 3 - 5 short-answer questions
    • Precise Matlab syntax will only matter at the “what I expect” vs “perfect” level
    • Full class period
    • Open book, notes, computer; closed person
• Questions?
• meshgrid for Building Function Tables
  • Problem: need to compute some expression on all pairs from 2 vectors
    
  • meshgrid constructs 2 matrices to use as pairs
    

    >> x = 1 : 5
    x =
         1     2     3     4     5
    >> y = 1: 5
    y =
         1     2     3     4     5
    >> [ A, B ] = meshgrid( x, y )
    A =
         1     2     3     4     5
         1     2     3     4     5
         1     2     3     4     5
         1     2     3     4     5
         1     2     3     4     5
    B =
         1     1     1     1     1
         2     2     2     2     2
         3     3     3     3     3
         4     4     4     4     4
         5     5     5     5     5
    >> A .* B
    ans =
         1     2     3     4     5
         2     4     6     8    10
         3     6     9    12    15
         4     8    12    16    20
         5    10    15    20    25
    >> x
    x =
         1     2     3     4     5
    >> z = [ 10 20 30 40 ]
    z =
        10    20    30    40
    >> [ C, D ] = meshgrid( x, z )
    C =
         1     2     3     4     5
         1     2     3     4     5
         1     2     3     4     5
         1     2     3     4     5
    D =
        10    10    10    10    10
        20    20    20    20    20
        30    30    30    30    30
        40    40    40    40    40
    >> C .* D
    ans =
        10    20    30    40    50
        20    40    60    80   100
        30    60    90   120   150
        40    80   120   160   200

• While Loops
  • Sections 12.1 and 12.2
    • Relational operators (<, >, <=, >=, ==, ~=)
      • Beware == vs =
    • while loop
      • Syntax:
        

        while expression
            …
        end

      • Execute code inside loop as long as expression is true
    • Control-C stops infinite loops
  • Example: Approximate base 10 logarithms by dividing by 10 until number ≤ 1
    • Algorithm
      

      x = some positive integer
      log = 0
      while x > 1
          x = x / base
          log = log + 1

      • Example of pseudocode
    • Matlab code
      

      x = 100;
      myLog = 0;
      while x > 1
          x = x/10;
          myLog = myLog + 1;
      end

• Next
  • Matlab input and output commands
    • input
    • fprintf
  • Logic in Matlab
    • Read section 13.3

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