SUNY Geneseo Department of Mathematics

Variables and Types

Wednesday, September 3

Math 230 01
Fall 2014
Prof. Doug Baldwin

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Misc
- NSF Fellowship workshop
  - Thursday, Sept. 4
  - 5:30 PM
  - South 338
Matlab’s User Interface
- 10 - 4 - 2
  - Matlab evaluates subtraction left-to-right as expected
  - But it could have been defined to evaluate right-to-left
  - Use parentheses to change evaluation order
- x = 1
  - Creates a variable named “x”
Variables and Expressions
- Sections 1.3 and 1.4
  - What is a variable?
    - Means (place) of storing a value
    - But places to store values aren’t the same as variables in math
    - x = y + 1 in Matlab means to fetch a value from y, calculate with it, and put a value into x, it doesn’t describe a permanent relationship between x and y
  - What is a type?
    - Operations only make sense for certain kinds of value
      - 3 + 8 makes sense because addition “works” on numbers
      - 3 + “good morning” doesn’t, because addition doesn’t work on phrases
    - type = set of values that share certain operations
      - Real numbers (aka floating point, single vs double precision)
      - Integers
      - Characters
      - Logical
    - Casting = converting between types
    - Some Matlab examples illustrating types
```
>> x = 1
x =
    1
>> whos
  Name      Size            Bytes  Class     Attributes
  x         1x1                 8  double
>> y = int32(x)
y =
    1
>> whos
  Name      Size            Bytes  Class     Attributes
  x         1x1                 8  double
  y         1x1                 4  int32
>> y / 2
ans =
    1
>> x / 2
ans =
    0.5000
>> phrase = 'good morning'
phrase =
good morning
>> whos
  Name        Size            Bytes  Class     Attributes
  ans         1x1                 8  double
  phrase      1x12               24  char
  x           1x1                 8  double
  y           1x1                 4  int32
```
    - Types have ranges
  - Numeric operations
    - Random number generation
  - Keywords?
    - e.g., for, if
Next
- Continue variables and expressions lesson

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