Index operations

[RobolabGs2]

Our matrix and vector throw exceptions in with cases, but standard:

irb(main):008:0> require 'matrix'
=> true
irb(main):009:0> v = Vector[1, 2, 3]
...
rb(main):018:0> v[-4]
=> nil
irb(main):019:0> v[-4] = 4
...
IndexError (given index -4 is outside of -3...3)
irb(main):020:0> v[-3] = 4
=> 4
irb(main):021:0> v
=> Vector[4, 2, 3]
irb(main):022:0> v[3] = 40
...
IndexError (given index 3 is outside of -3...3)
irb(main):014:0> m = Matrix[[1, 2], [3, 4]]
=> Matrix[[1, 2], [3, 4]]
irb(main):015:0> m[-1, -2]
=> 3
irb(main):016:0> m[-1, -3]
=> nil