SUNY Geneseo Department of Mathematics

Basic Matlab Expressions

Monday, January 26

Math 230 02
Spring 2015
Prof. Doug Baldwin

Misc
- Workshop for students interested in applying to REUs
  - Today (January 26), 5:30 PM
  - South 328
  - Prof. Macula
- Nick’s office hours moved to Wednesday, 6:00 - 7:00, same place (Fraser 213)

Questions?

Random integers in Matlab?

>> randi( 1, 100 )
ans =
    … many lines of 1s …
>> help randi
    … description of how to use randi …
>> randi( [1,100], 1 )
ans =
    16
>> randi( [1,100], 1 )
ans =
    97
>> rand
ans =
    0.8763
>> rand * 100
ans =
    48.8629
>> floor( rand * 100 )
ans =
    40
>> round( rand*100 )
ans =
    13
>> ceiling( rand*100 )
{Undefined function 'ceiling' for input arguments of type 'double'.} 
>> ceil( rand*100 )
ans =
     1
>> randi( [1,100] )
ans =
    19
>> randi( [1,100], 5 )
ans =
    33    34    27    29     8
     6    24    84    27     6
    15    46    70    26    26
    73    19    34    68    44
    49    33    59    52    29

Matlab as Calculator
- Sections 1.1, 1.2, 1.4
  - Different commands, e.g.,
    - help
    - help help
  - Output can be formatted, e.g., tighter vs looser spacing
  - Random number generator
  - Special names, e.g.,
    - inf = infinity
  - Operator symbols and functions
  - Window layout
- Examples
  - diary command records commands and output to a file
  - Add/subtract/multiply/divide/exponentiate etc.
    - Beware that computers only have finite precision for real numbers, round-off error
```
>> pi + 1
ans =
    4.1416
>> format long
>> pi + 1
ans =
    4.141592653589793
>> 1 + inf
ans =
    Inf
>> 1e9 + 1
ans =
    1.000000001000000e+09
>> 1e100 + 1
ans =
    1.000000000000000e+100
>> 3 + 5 * 9
ans =
    48
>> (3+5) * 9
ans =
    72
>> % This is a comment
```
  - A more complex expression: the derivative of sin^-1x is 1 / √(1-x²). What is the value of this expression when x = π/4?
```
>> x = pi / 4
x =
    0.785398163397448
>> 1 / √(1-x^2)
 1 /√(1-x^2)
     |
{Error: The input character is not valid in MATLAB statements or expressions.} 
>> 1 / sqrt(1-x^2)
ans =
    1.615532655169348
```
Next
- Variables
- Read section 1.3
- Optional: Variables part (first 2 3/4 minutes) of “Variables and Simple Arrays” video from Edinburgh
  - http://www.see.ed.ac.uk/teaching/courses/matlab/unit01/variables-arrays.shtml

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