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— gibson:teaching:fall-2014:math445:lecture1-diary [2014/09/02 07:03] (current)
gibson created
Line 1: Line 1:
 +<​code>​
 +% =========================================================
 +% Basic matlab usage: ​
 +% type in expression, matlab computes, and returns answer
  
 +7 + 8 * 6
 +
 +ans =
 +    55
 +
 +(7 + 8) * 6
 +
 +ans =
 +    90
 +
 +% arithmetic operations are
 +% + - * / ^ 
 +
 +% here's how to compute 3 squared, i.e. 3 to the 2
 +
 +3^2 
 +
 +ans =
 +     9
 +
 +% =========================================================
 +% Variables ​
 +
 +% assign a number into a variable
 +
 +x = 5 % assign the value 5 into the variable x
 +
 +x =
 +     5
 +
 +x
 +
 +x =
 +     5
 +
 +2+x
 +
 +ans =
 +     7
 +
 +% Assign 9 + 2*4 (that is, 17) into the variable x
 +x = 9 + 2*4 
 +
 +x =
 +    17
 +
 +% Note: this is not an equation! It's an assignment of a value into a variable.
 +x = 9 + 2*4 
 +
 +x =
 +    17
 +
 +
 +% Note: Matlab can be '​cute'​
 +
 +% "​who"​ tells what variables matlab knows at any time
 +who 
 +
 +Your variables are:
 +
 +ans  x    ​
 +
 +% "​whos"​ is a more detailed version of "​who",​ tells type (class) as well
 +whos
 +  Name      Size            Bytes  Class     ​Attributes
 +
 +  ans       ​1x1 ​                ​8 ​ double ​             ​
 +  x         ​1x1 ​                ​8 ​ double ​             ​
 +
 +
 +% convert x to an integer and store in n. "​uint32"​ is unsigned 32-bit integer
 +n = uint32(x); ​
 +
 +whos
 +  Name      Size            Bytes  Class     ​Attributes
 +
 +  ans       ​1x1 ​                ​8 ​ double ​             ​
 +  n         ​1x1 ​                ​4 ​ uint32 ​             ​
 +  x         ​1x1 ​                ​8 ​ double ​             ​
 +
 +% The default type (class) of any variable is double (double precision ​
 +% floating point number)
 +
 +
 +y = exp(23) % compute e^23
 +
 +y =
 +   ​9.7448e+09
 +
 +% this is standard text notation for 9.7448 x 10^9
 +
 +y = exp(-23) % compute e^23
 +
 +y =
 +   ​1.0262e-10
 +
 +% this is standard text notation for 1.0262 x 10^-10
 +
 +whos
 +  Name      Size            Bytes  Class     ​Attributes
 +
 +  ans       ​1x1 ​                ​8 ​ double ​             ​
 +  n         ​1x1 ​                ​4 ​ uint32 ​             ​
 +  x         ​1x1 ​                ​8 ​ double ​             ​
 +  y         ​1x1 ​                ​8 ​ double ​             ​
 +
 +% class(variable) tells you the class (type) of a variable
 +class(x)
 +
 +ans =
 +double
 +
 +% ===============================================================
 +% logical expressions
 +
 +% 3 > 1 is a logical expression, just like 3 + 1 is an arithmetic expression
 +
 +3 > 1 
 +
 +ans =
 +     1
 +
 +% in matlab, true is 1 and false is 0
 +
 +% this is a logical expression, just like 3 + 1 is an arithmetic expression
 +3 < 1 
 +
 +ans =
 +     0
 +
 +% evaluate 3 > 2 to true (1) and assign to variable b
 +b = 3 > 2 
 +
 +b =
 +     1
 +
 +class(b)
 +
 +ans =
 +logical
 +
 +whos
 +  Name      Size            Bytes  Class      Attributes
 +
 +  ans       ​1x7 ​               14  char                 
 +  b         ​1x1 ​                ​1 ​ logical ​             ​
 +  n         ​1x1 ​                ​4 ​ uint32 ​              
 +  x         ​1x1 ​                ​8 ​ double ​              
 +  y         ​1x1 ​                ​8 ​ double ​              
 +
 +% illustrate && (and) and || (or)
 +
 +
 +3 > 2 && 4 > 1        % this means 3 > 2 AND 4> 1
 +
 +ans =
 +     1
 +
 +3 > 2 && 4 < 1        % this means 3 > 2 AND 4 < 1
 +
 +ans =
 +     0
 +
 +% Implicit type conversion, will convert logical true (1) to 1 to add to 18
 +
 +(3 > 2 && 4 > 1) + 18 
 +
 +ans =
 +    19
 +
 +
 +3 > 2 || 4 > 1        % this means 3 > 2 OR  4 > 1
 +
 +ans =
 +
 +     1
 +
 +3 > 2 || 4 < 1        % this means 3 > 2 OR  4 < 1
 +
 +ans =
 +
 +     1
 +
 +3 < 2 || 4 < 1        % this means 3  < 2 OR  4 < 1
 +
 +ans =
 +     0
 +
 +
 +
 +% ~ means NOT, logical inversion
 +
 +~1       % not true, ie false
 +
 +ans =
 +     0
 +
 +~0       % not false, ie true
 +
 +ans =
 +     1
 +
 +3 > 2 
 +
 +ans =
 +     1
 +
 +~(3 > 2)
 +
 +ans =
 +     0
 +
 +~(3 < 2 || 4 < 1)        % this means NOT (3  < 2 OR  4 < 1)
 +
 +ans =
 +     1
 +
 +</​code>​
gibson/teaching/fall-2014/math445/lecture1-diary.txt ยท Last modified: 2014/09/02 07:03 by gibson

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