# Roll back random generator

``

    rand_back  amount (number)

Roll the random generator back essentially ‘undoing’ the last call to `rand`. You may specify an amount to roll back allowing you to skip back n calls to `rand`.

Introduced in v2.7

## Examples

# Example 1
``
      puts rand

      rand_back

      puts rand
      puts rand
| ``
    # Basic rand stream rollback

    # prints 0.75006103515625

    # roll random stream back one
    # the result of the next call to rand will be
    # exactly the same as the previous call

    # prints 0.75006103515625 again!
    # prints 0.733917236328125
# Example 2
``
      puts rand
      puts rand
      puts rand
      puts rand

      rand_back(3)

      puts rand
      puts rand
| ``
    # Jumping back multiple places in the rand stream

    # prints 0.75006103515625
    # prints 0.733917236328125
    # prints 0.464202880859375
    # prints 0.24249267578125

    # roll random stream back three places
    # the result of the next call to rand will be
    # exactly the same as the result 3 calls to
    # rand ago.

    # prints  0.733917236328125 again!
    # prints  0.464202880859375