


Section 3: Automatic Memory Stack and ALPHA Register54


Example. A bacteriologist tests a certain strain
whose population typically increases by 15% each day
(a growth factor of 1.15). If he starts a sample culture
of 1000, what will be the bacteria population at the end
of each day for five consecutive days?


Method: Put the growth factor (1.15) in the Y,
Z, and Tregisters and put the original population
(1000) in the Xregister. Thereafter, you get the
new daily population whenever you press
× .






1.15 _

1.15000

1.15000

1.15000

1000 _

1,150.0000

1,322.5000

1,520.8750

1,749.0063

2,011.3572



When you press × the first time, you
calculate 1.15 × 1000. The result (1,150) is displayed in the
Xregister and a new copy of the growth factor drops into the Yregister.
Since a new copy of the growth factor is duplicated from the Tregister each
time the stack drops, you never have to reenter it.


Notice that performing a twonumber operation such as
× causes the number in the Tregister to be
duplicated there each time the stack is dropped. However, the
R function simply rotates the contents of the stack
registers; it does not rewrite any number, but merely shifts the numbers that
are already in the stack.



