HP HP-18C - Page 176

Figure B-1. Displaying the Current Estimates During a
Numerical Calculation.
CALCULATING ...
AP1:3.19258240357
AP1: 0. 07000000000
DIII1:Ili
Sign of
+ } LEFT - RIGHT for
each estimate
Since calculators cannot do calculations with infinite precision (the
HP -18C uses 12 digits in its calculations), sometimes the solver will be
unable to find an estimate where LEFT - RIGHT is exactly o. How-
ever, the solver can distinguish between situations where the current
estimate may be a solution, and situations where the solver cannot
find a solution .
The search for a numerical solution can sometimes take several min-
utes. (You can halt the search at any time by pressing any key .) There
are four possible outcomes for a numerical solution :
• Case 1: The HP-18C displays an answer on line 3 and there is no
message in lines 1 and 2. It is very likely that the answer on line 3
is a
solution for the unknown variable.
There are two situations in which the solver returns a case 1 an-
swer (see figure B-2):
• Case
1a : LEFT-RIGHT is exactly O .
• Case 1 b: LEFT - RIGHT is
not zero for either estimate . However,
the solver has found two estimates that cannot get any closer
together.
(Numbers that are as close together as possible are
called "neighbors.") Furthermore, LEFT - RIGHT is a positive
value for
one estimate and a negative value for the other
estimate .
174 B: More About HP-18C Calculations