Miscellaneous Vector Features

Return to List of Lectures

Previous Lecture

• Misc
  • MLC has tutors on duty specifically knowledgeable about this course
    • Mon: 10:30-11:30, 1-2, 7-8:30
    • Tues: 12:30-3:30, 7-10
    • Wed: 10:30-11:30, 1-2:30, 7-10
    • Thurs: 2-3:30, 7-10
    • Fri: 10:30-11:30, 1-2:30
  • Matlabs without findpeaks function?
    • Try re-downloading and re-installing Matlab
    • Use help findpeaks to see if you have it
      

      >> help findpeaks
       findpeaks Find local peaks in data
          …

• Questions?
• Advanced Vector Topics
  • Sections 5.7 - 5.9
    • Indexing with arrays
      • array( int ) picks element at position int
      • array( int1:int2) picks out elements from positions int1 to int2
    • Resize array by assigning to position beyond end
      • array( n ) = value
      • Spaces between end of array and n fill with 0
    • Concatenation combines 2 arrays
      • [ array1, array2 ]
    • Delete elements by setting them to []
    • size() gives you the size of an array
    • end indexes end element in array
      • Also end-1, end-2, etc.
  • Examples
    • Reverse a vector
      

      >> v = [ 1 3 5 7 9 11 ]
      v =
          1     3     5     7     9    11
      >> a = v( end:-1:end-6 )
      Subscript indices must either be real positive integers or
      logicals. 
      >> a = v( end:-1:end-5 )
      a =
          11     9     7     5     3     1
      >> a = fliplr( v )
      a =
          11     9     7     5     3     1
      >> a = v( end:-1:1 )
      a =
          11     9     7     5     3     1
      >> % Rearrange a vector, e.g., to be in sorted order
      >> v = [ 4 2 8 9 1 ]
      v =
          4     2     8     9     1
      >> v( [ 5 2 1 3 4 ] )
      ans =
          1     2     4     8     9

    • Find the size of a vector. Find out only how many columns it has.
      

      >> size( v )
      ans =
          1     5
      >> length( v )
      ans =
          5
      >> s = size( v )
      s =
          1     5
      >> s(2)
      ans =
          5
      >> [r c] = size( v )
      r =
          1
      c =
          5

    • Growing list of favorite numbers
      

      >> numbers = [ 17 ]
      numbers =
          17
      >> numbers(2) = 82
      numbers =
          17    82

    • Expand a vector to contain 8 copies of its original value, end-to-end
      

      >> numbers = [ numbers, numbers ]
      numbers =
          17    82    17    82
      >> numbers = [ numbers, numbers ]
      numbers =
          17    82    17    82    17    82    17    82
      >> numbers = [ numbers, numbers ]
      numbers =
        Columns 1 through 10
          17    82    17    82    17    82    17    82    17    82
        Columns 11 through 16
          17    82    17    82    17    82

• Vector Lab
• Next
  • “Reduce” operations on vectors, column vectors
    
  • Read sections 7.9 and 5.14

Next Lecture