Re: HP48 vs TI-92


[Prev][Next][Index][Thread]

Re: HP48 vs TI-92



Al Arduengo wrote:
>
> Here is a little something for 92 owners. Try the following limit problem:
>
>         -s*t
> Lim    e    *t
> t->inf ---------|s=s
>            2
>          s
>
> ie The limit of exp(-s*t)*t/s^2 as t approaches infinity where s equals s.
> Careful though. It nuked me in one case (I lost all memory) and gave a
> mem error in another case. For your info, it is the "where" statement
> that caused the problem. Change it to s=n and all is fine. Is this
> problem apparent on all 92s or just mine?
>
> Also, limits do not work well if the expression being limited involves a
> product or quotient of mre than one variable. ie e^(-s*t) as t approaches
> infinity returns undef where e^(-s+t) returns zero. Anyone know a way
> around this?
>
>                   ,-vvv----,
>           o--vvv--+---|\   |
>                   ____| >o-'--< Al Arduengo
>                  _+_  |/
>                   -
Yes, you have to restrict the calculation for the case s>0 otherwise
the expression is divergent. The other problem that you had when you
were using the restriction s=s is not surprising. The computer
probably substitute s for s recursively until the memory filles up.


Now when I am on the thread I would like to give my own opinions
about the TI-92. I have great use of it in my research work
especially the powerful and easy-to-use symbolic math processor. I
believe that a QWERTY layout and fairly large screen is necessary to
make such calculations usable. The advantage of having a separate
symbolic math calculator compared to using Maple, Mathematica or
Derive on my computer is that the TI-92 is very portable, have
constant memory, no booting up time and very long battery life. I
measured the current consumption to 4.5-7 mA in "low power" mode and
35-45 in "idle" mode depending on the battery voltage (5-6V). This
is quite impressive since it is about the power consumption of a
single commercial low-power version of 68000 processor (MC68HC000)
without any memory and screen drivers.


But some things with the TI-92 annoys me that doesn't make it "The
Perfect Calculator". It is annoyingly slow when it comes to
numerical calculations compared to other calculators like HP-48,
TI-85 and even the high-end CASIO's. This is surprising with such a
powerful processor at 10 MHz. I also don't understand why the speed
slows down remarkably (more than 10%) when the history file gets
larger compared when it is empty.


I would have prefered to have more of the Derive package installed
instead of the Cabri geometry program which has very limited use
outside school. I found a demo-version of Cabri II for Macintosh on
the net that made me understand its potential as a pedagogical tool.
But I believe that the speed is too low and the screen too small and
slow on the TI-92 to utilise it even for such purposes. I would have
instead prefered built-in powerful routines for solving differential
equations and nonlinear equation systems like the one in the freely
available advanced math library for TI-92 from Soft Warehouse. But
these optional packages take a lot of valuable RAM. Does anyone know
if the TI-92 operative system supports the extra RAM-slot. The
memory type and package is very popular and commercially available
from Toshiba so it would be no problem to put in an extra 128k.


I have ROM version 1.11 from 04/11/96. There are still some bugs. A
couple of times the TI-92 has crashed, sometimes with error messages
at the top of the screen (e.g. "illegal address") and I have had to
reset the calculator with all my programs. I have not yet been able
to find the cause of these crashes since the seem to happen
randomly. It is probably some problem with memory management and
this has to be fixed or the user is more or less forced to buy (or
build) a link cable. By the way, is there anyone who has managed to
build a cable for the TI-92 that works with a Mac? I don't want to
pay the high price for the original TI-cable (more than $100 in
Sweden).


Another thing that annoys me is that it is not possible to use the
Ti-92 like an "ordinary" calculator with single-stroke functions
instead of using these annoying parantheses. As now I often use
another calculator for such simple numerical calculations.


But still with these drawbacks I think that the TI-92 is an amazing
calculator that fulfills a need in the days of laptop computers. The
symbolic math program and user interface (including the screen and
QWERTY keyboard) is superior compared with the HP 48 and makes it a
useful tool in proffesional life. If you don't work full time with
the HP-48 you need the handbook with you to remember all the
functions. The HP-48 is therefore more suitable for people that want
to have the calculator as a full time hobby with its many
difficult-to-find functions and low-level programming. I have great
use of the TI-92 matrix and complex math arithmetic (even if the
matrix calculations are truly annoyingly slow). The handbook is well
written and very well translated to swedish. By the way I have found
a list of some (18) of the persons involved in the TI-92 by pressing
[F5] [diamond] [(] [P]. I think they have all in all done a great
job.


Dr. Richard Schatz
Laboratory of Photonics and Microwave Eng.
Royal Institute of Technology
Stockholm


References: