HP 48g Graphing Calculator - Manual (Page 356)

25
Interpreting Results from the Multiple Equation Solver
The Multiple-Equation Solver solves for variables by repeatedly
looking through the set of equations for one that contains only one
variable that’s “unknown” (not user-defined and not found by the
solver during this solution)—then it uses the HP 48 root-finder to find
that value. It continues eliminating “unknown” variables until it solves
for the variable you specified—or until it can’t solve for any more
variables. Each time the Multiple-Equation Solver starts solving for a
variable, only the variables with black menu labels are “known.”
During the solution process, the Multiple-Equation Solver shows the
variable it’s currently solving for. It also shows the type of root found
by the HP 48 root-finder (zero, sign reversal, or extremum)—or the
problem if no root is found (bad guesses or constant). (You can
watch the iterations if you press any key except (CANCEL ) during the
root-finding process. For more information about the root-finder, see
chapter 18.
The following messages indicate errors in the problem setup:
■ Bad Guess <ea). Units may be missing or inconsistent for a
variable. For a list of guesses, at least one of the list elements must
have consistent units,
■ Too |■ ‘1.эny Unknowns. The solver eventually encountered only
equations having at least two unknowns. Either enter other known
values, or change the set of equations—whichever is appropriate for
your problem. See “Changing the Equations” later in this chapter.
■ Constant? The initial value of a variable may be leading the
root finder in the wrong direction. Supply a guess in the opposite
direction from a critical value—if negative values are valid, try one.
Checking Solutions
The variables having a a: mark in their menu labels are related for the
most-recent solution—they form a compatible set of values satisfying
the equations used. The values of any variables without marks may
not satisfy the equations because those variables weren’t involved in
the solution process.
If any solutions seem improper, check for the following problems:
25-10 The Equation Library