Texas Instruments TI-92+, Tip List

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For example, suppose the current equation is a=b+c, then the complete entry line looks like this before
the final [ENTER] is pressed:
util\delvar 1 (util\exprvars("a=b+c"))
If eqn is an expression instead of an equation, then eqn has the form exp = expression, where exp is a
system variable. This method will delete exp along with the other variables, since exprvars() includes
exp in the variable list.
The method can be automated with this program:
deleqnv()
Prgm
©Delete vars in eqn
©28dec0
1 /dburkett@infinet.com
local ö,ü
Try:newFold(ä):else:endTry © Create new folder if necessary
setFold(ä) → ö © Make new folder current & save old folder
string(eqn) → ü © Convert eqn to string, without var substitution
setFold(#ö) © Restore old folder
util\delvar 1 (util\exprvars(ü)) © Extract eqn variables & delete them
EndPrgm
deleqnv() calls delvar1() and exprvars(), both of which must be in the util\ folder. The bulk of the
program recovers eqn as a string without variable substitution. For more details on this method, see tip
[7.40], Recall expression without variable value substitution. delvar1() is described in tip [7.39], Quickly
delete locked, archived variables. exprvars() is described in tip [7.42], Find variable names used in
expressions.
This program will not work if you change folders after using the numeric solver.
[6.55] Algorithms for factor() and isPrime()
The following description of the algorithms for factor() and isPrime() was obtained from TI by
Bhuvanesh Bhatt. It is included with TI's permission.
"The algorithms used in the TI-92, TI-92 Plus, and TI-89 are described in D. Knuth, The Art of
Computer Programming, Vol 2, Addison-Wesley, but here is a brief description:
"The TI-92 simply divides by successive primes through the largest one less than 2^16.1: It doesn't
actually keep a table or use a sieve to create these divisors, but cyclically adds the sequence of
increments 2, 2, 4, 2, 4, 2, 4, 6, 2, 6 to generate these primes plus a few extra harmless composites.
"TI-92 Plus and TI-89 start the same way, except that they stop this trial division after trial divisor 1021,
then switch to a relatively fast Monte-Carlo test that determines whether the number is certainly
composite or is almost certainly prime. (Even knowing the algorithm, I cannot construct a composite
number that it would identify as almost certainly prime, and I believe that even centuries of continuous
experiments with random inputs wouldn't produce such a number).
"The isPrime() function stops at this point returning either false or (almost certainly) true.
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