CAS simplifying non-zero expressions to 0

[kickniko]

Hi Nigel,

and thanks for being helpfully unhelpful!

(10-06-2014 11:08 AM)Nigel (UK) Wrote:  I've noticed this before. As a physicist small numbers are a completely normal part of my work and are not an indication of rounding error. I find this behaviour a real obstacle to whole-heartedly embracing the Prime in my teaching and to recommending it to my physics students.

Same with me, more or less, Nigel. Since some days I try to finish the design of an HF-amp stage for my business, and small floats are a completely normal part of the job. It may be "only" a coefficient of 6.0929985e-32 for Omega^8, but Omega runs up to 10^6 (and so f even more).

(10-06-2014 11:08 AM)Nigel (UK) Wrote:  To work around it, you can replace approximate numbers by exact numbers (e.g., write 663/100 * 10^{-34} for Planck's constant) or use symbols that you then substitute numerical values for at the end of a calculation, but neither approach is anywhere near convenient in all circumstances.

This is exactly what I was trying to do. Formulate complex Z as a function of all participating circuitry variables, make some assumptions for helping the CAS, then let it find the magnitude of Z, substitute real values, and then simplify/expand for getting some more "pleasant" expression for the plotter. (Or else plotting takes for ever.) But after substitution and simplification I got the (unwished) conversion of small coeffs of Omega to 0.

Substituting with exact numbers instead of floats ends up with the calc hanging or crashing - I guess the expression for abs(Z) gets too big for it then, as it is about 33K already with floats. Not necessary to mention that I don't have any intention to edit such an expression manually - or what did I buy the Prime for? (And this was also why I was asking about commands for decomposing and composing expressions in my other post).

So, as you say, how could somebody not develop quite an ambivalent opinion about the Prime?....

(10-06-2014 11:08 AM)Nigel (UK) Wrote:  I would really like to see this truncation of small quantities as an optional function to be applied when and if I choose to do so (like Chop[] in Mathematica, if my memory serves me correctly). I think it is no more logical to replace small numbers by zero by default than it is to replace numbers greater than three by the string "many"!

Exactly! The many auto-assumptions of the makers about the work of other people are becoming a boomerang against their own machine that could have been fantastic otherwise. Even for example the pre-definition of home variables but without any kind of folders is a big obstacle for work beyond the level of "exploration of the quadratic equation". (What a fancy terminology! "Exploration"!!!!)

I will have to search some other way to work out such things on the Prime, but if the search evolves to a dissertation work for itself, then it is obvious that something is wrong already in the concepts of the calculator. For I did not buy it in order to change my profession to IT/CAS-specialist, but rather as a help for my own business.

Still hoping. Ciao,

Nick