|Re: A derfinition of CAS/Computer Algebra System, please.|
Message #3 Posted by Albert Graef on 6 Dec 2001, 9:53 p.m.,
in response to message #1 by Matt Agajanian
Well, actually the acronym stands for Calculator Algebra System (IIRC). The 48/49 has a builtin data type for representing symbolic expressions/formulas (called "algebraics"). It also has an editor which allows you to enter algebraic expressions in a format close to textbook-style formatting. The CAS is a set of functions operating on such algebraics, to perform symbolic simplifications, compute symbolic derivatives/integrals and solve symbolic equations. It can even compute the eigenvalues of symbolic matrices. The kind of stuff you'd otherwise have to do on a sheet of paper. You can also apply most of these functions right away in the equation writer.
I still remember how I was puzzled the first time I turned on my brand-new 49G, entered the calculation PI 4 / SIN, and got the result 'SQRT(2)/2'. ;-) That happens because the calc, by default, is operating in "exact" (as opposed to "approximate", i.e., numeric) mode and therefore tries to compute the exact result using symbolic simplifications. If that doesn't work out (i.e., you typed an expression which cannot be simplified), you can still get the numeric result quickly with the ->NUM function. Or you switch over to approximate mode and get the usual numeric results right away.
A tutorial listing (almost) all commands the 49G CAS, with simple examples, is available here: http://www.hpcalc.org/details.php?id=4562. And of course there are Gilberto Urroz' books, I already gave the reference in another thread.