Introduction to Matlab Vectors

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• Misc
  • Math colloquia
    • Leary, “Axioms, Models, Infinity, and the Nature of the Universe”
      • Thursday, Feb. 5, 2:30 - 3:30, Newton 203
    • Dickerson, “Mathematics Majors’ Understandings of the Concept of Mathematical Definition”
      • Monday, Feb. 9, 4:00 - 5:00, Newton 201
    • Extra credit for going and writing summary/reaction to either or both
• Questions?
• Vectors and Matrices
  • Section 2.1
    • Create vectors and matrices
      • Colons to make rows
      • Semicolon to separate rows in matrix
      • Can make vectors with steps between values
        • e.g., 1:2:9 is 1, 3, 5, 7, 9
        • linspace = linearly spaced elements
        • logspace = logarithmically spaced elements
      • How to enter matrices
      • Extending vectors by adding to end
    • Accessing elements
      • Picking elements from matrices via indexing
      • Assigning new values to elements
        • Modify elements by assigning to indexed element
    • Operations on matrices
      • Functions to find length, size of matrices
      • Also ways to flip, rotate, transpose matrices
      • Reshaping matrices
    • Can have empty vectors either for creation or for deletion
  • Examples
    

    % 5-by-5 linearly spaced values between 0 to 5
    >> m = linspace(0,5,5)
    m =
        0    1.2500    2.5000    3.7500    5.0000
    >> m = [ linspace(0,5,5); linspace(0,5,5); linspace(0,5,5); linspace(0,5,5); linspace(0,5,5) ]
    m =
        0    1.2500    2.5000    3.7500    5.0000
        0    1.2500    2.5000    3.7500    5.0000
        0    1.2500    2.5000    3.7500    5.0000
        0    1.2500    2.5000    3.7500    5.0000
        0    1.2500    2.5000    3.7500    5.0000
    % Not really what we wanted...
    >> values = linspace(0,5,25)
    values =
        Columns 1 through 6
            0    0.2083    0.4167    0.6250    0.8333    1.0417
        Columns 7 through 12
            1.2500    1.4583    1.6667    1.8750    2.0833    2.2917
        Columns 13 through 18
            2.5000    2.7083    2.9167    3.1250    3.3333    3.5417
        Columns 19 through 24
            3.7500    3.9583    4.1667    4.3750    4.5833    4.7917
        Column 25
            5.0000
    >> reshape( values, 5, 5 )
    ans =
             0    1.0417    2.0833    3.1250    4.1667
        0.2083    1.2500    2.2917    3.3333    4.3750
        0.4167    1.4583    2.5000    3.5417    4.5833
        0.6250    1.6667    2.7083    3.7500    4.7917
        0.8333    1.8750    2.9167    3.9583    5.0000
    % We want values to progress across rows, not down columns
    >> ans'
    ans =
             0    0.2083    0.4167    0.6250    0.8333
        1.0417    1.2500    1.4583    1.6667    1.8750
        2.0833    2.2917    2.5000    2.7083    2.9167
        3.1250    3.3333    3.5417    3.7500    3.9583
        4.1667    4.3750    4.5833    4.7917    5.0000
    >> % Indexing -- picking one or more values out of a matrix or vector
    >> m = ans;
    >> values(17)
    ans =
        3.3333
    >> values(15:19)
    ans =
        2.9167    3.1250    3.3333    3.5417    3.7500
    >> values( [3 8 12 2 3] )
    ans =
        0.4167    1.4583    2.2917    0.2083    0.4167
    >> m
    m =
             0    0.2083    0.4167    0.6250    0.8333
        1.0417    1.2500    1.4583    1.6667    1.8750
        2.0833    2.2917    2.5000    2.7083    2.9167
        3.1250    3.3333    3.5417    3.7500    3.9583
        4.1667    4.3750    4.5833    4.7917    5.0000
    >> m( 15:19 )
    ans =
        4.5833    0.6250    1.6667    2.7083    3.7500
    >> m( 3, 3 )
    ans =
        2.5000
    >> m( 4:5, 4:5 )
    ans =
        3.7500    3.9583
        4.7917    5.0000

• Next
  • Calculations on vectors and matrices
  • Read sections 2.2 and 2.3
  • Optionally watch “The Dot Operator” video at http://www.see.ed.ac.uk/teaching/courses/matlab/unit01/dot-operator.shtml

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