Variables and Arrays

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Chapter 2

• Variables and Arrays

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• http//web.njit.edu/vge2
• website updated.

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Array

• It is the fundamental unit of data in any MATLAB
  program.
• An array is a collection of data values organized
  into rows and columns, and known by a single name.

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Arrays

• Individual data values within an array are
  accessed by including the name of the array
  followed by subscripts in parentheses that
  identify the row and column of the particular
  value.
• Single dimensional arrays ? vectors
• Two or more dimensions arrays ? matrices
• Size of an array is specified by the number of
  rows and the number of columns in the array, with
  the number of rows mentioned first.
• Total number of elements in the array will be the
  product of the number of rows and number of
  columns
• Store the elements by column-wise in memory.

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Arrays
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Arrays
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Arrays example
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variable

• It is a region of memory containing an array,
  which is known by a user-specified name i.e. a,
  b, c in the previous example.
• Variable names are case-sensitive.
• MATLAB variable names must begin with a letter,
  followed by any combination of letters, numbers
  and the underscore( _ ) character.
• Names with more than 63 characters are truncated
  to 63.

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Variable types

• Double - principle data type in MATLAB.
• Holds real, imaginary, or complex values.
• Real and imaginary numbers can be in the
  range 10-308 to 10308 with 15 to 16 significant
  decimal digits of accuracy.
• e.g. Real var 10.5, imaginary var
  4i,
• complex number var 1010i
• Char - holds character strings
• e.g. varThis is a character string
• (note place the characters in between
  single quotes)

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Creating arrays
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Creating arrays cont..

• empty matrix.
• Use comma (,) or space to separate elements in
  the same row.
• Use semicolon() to move to the next row.
• Note All rows must have the same number of
  columns.
• Arrays can be initialized using algebraic
  operations and all of or portions of previously
  defined arrays.
• e.g. a0 17 ? a0 8
• ba(2) 7 a ? b8 7 0 8

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Creating arrays cont..

• Not all of the elements in an array must be
  defined when it is created.
• eg c(2,3)5 -gt c 0 0 0 d1,2
  d(4)4 ?d1 2 0 4
• 0 0 5 ,

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Short cut expressions

• Colon () operator
• Short cut notation to create arrays
• General form first increment last
• eg x1210 ? x1 3 5 7 9
• Transpose () operator
• swaps the row and columns of any array that it is
  applied to.
• Useful to initialize column vectors and more
  complex matrices.
• eg f14 ? f 1 , g14 hg g ? h
  1 1
• 2
  2 2
• 3
  3 3
• 4
  4 4

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Initializing arrays with built-in functions
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Built-in functions cont

• eg azeros(2)
• bzeros(2,3)
• c1 23 4
• dzeros(size(c))

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Initializing variables with keyboard input

• input()
• eg in1 input(Enter data )
• Enter data 1.23
• ? stores the value 1.23 into in1
• in2 input(Enter data ,s)
• Enter data 1.23
• ? stores the character string 1.23 into in2

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subarrays

• eg

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end function

• eg arr31 2 3 4 5 6 7 8
• arr3(5end)?5 6 7 8 arr3(end)?5
• Value returned by end is always the highest value
  of a given subscript.

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Subarrays cont..
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Subarrays cont..

• Assigning scalar to an array
• arr41 2 3 4 5 6 7 8 9 10 11 12
• arr4(12,12)1
• ?arr4 1 1 3 4
• 1 1 7 8
• 9 10 11 12

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Predefined special values
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Exercise
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Exercise
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Exercise