Predefined values
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Lifted from Programming and Data Types: M-File Programming: Special Values:

ans      Most recent answer (variable). If you do not assign an output variable
         to an expression, MATLAB automatically stores the result in ans.
eps      Floating-point relative accuracy. This is the tolerance 
         MATLAB uses in its calculations.
realmax  Largest floating-point number your computer can represent.
realmin  Smallest floating-point number your computer can represent.
pi       3.1415926535897...
i, j     Imaginary unit.
inf      Infinity. Calculations like n/0, where n is any nonzero real value, 
         result in inf.
NaN      Not-a-Number, an invalid numeric value. Expressions like 0/0 and 
         inf/inf result in a NaN, as do arithmetic operations involving a NaN.
         n/0, where n is complex, also returns NaN.
computer Computer type.
version  MATLAB version string.
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Arrays:
+ scalar:  command
+ 1D:      command(1,size) or command(size,1)
+ 2D:      command(rows,cols) or command(size)   

+ Initial values:
  zeros  generate an array of zeros
  ones   generate an array of ones
  rand   generate an array of random numbers between (0,1)
         (does not include 0 and 1)

examples)

>> ones(3)

ans =

     1     1     1
     1     1     1
     1     1     1

>> rand(1,3)

ans =

    0.9501    0.2311    0.6068
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Random numbers:
+ use FLOOR or CEIL to force an endpoint and/or generate integers

  >> high = 10;
  >> low =  1;
  >> target = ceil(rand*(high-low)) + low
  >> target = floor(rand*(high-low+1)) + low
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