CAS simplifying non-zero expressions to 0

[kickniko]

(10-06-2014 04:27 PM)parisse Wrote:  Nick: Ok, take something else if you think you will find elsewhere.

You bet I know now what we will be using as a mobile tool.

(10-06-2014 04:27 PM)parisse Wrote:  That will not change the fact that rewriting your large expression as a rational fraction (that's what simplify does, and perhaps that's what you misunderstood) will return a big answer. If you need to plot this |Z|, writing it as a rational fraction is a bad idea, you should keep it as is (I wonder what kind of simplification you expected by the way).

Leaving it the way it was before trying to simplify it means to be left with a 1 over a huge square root of nested fractions of squares. And this is something for which I do not need such a tool. Turning it to a rational fraction, for example, would be of help for us for understanding a bit better what happens when Cvar varies, or similar things.

On with my expectations: I expected that simplification, after substituting the real values, would perhaps have the grace to bring it to the form of a fraction and to collect the many different numerical coefficients of like powers of Omega, something that already the 48 could do (but of course much slower). This is what I thought about simplifying in this case, since indeed there is not anything more to simplify, as you say. But simplification zeroed out very important terms of the polynomials on both numerator and denominator, and made the expression simply wrong.

Further expectations: I thought that simplifying first and then substituting real values would do better job. But unfortunately it has the disadvantage that you end up without collection of like powers. The result is a sum of powers of Omega both on the numerator as also on the denominator, but unfortunately not of the form

a(n)*Omega^n+a(n-1)*Omega^(n-1)+...+a0

but rather

a(n)*Omega^n+b(n)*Omega^n+c(n)*Omega^n+...
a(n-1)*Omega^(n-1)+b(n-1)*Omega^(n-1)+c(n-1)*Omega^(n-1)+....

where all the a, b, c.... are real numbers. If you then try to simplify, of course the same powers of Omega as before disappear again. If you stay with the above result... Well, let's say it is correct and, lets say it is usable then. At least it can be put into the plotter and be plotted, if one has the money to invest for... waiting and for having to do collection of coefficients of like powers by hand. Sorry HP, sorry Tim, and sorry Bernard, I am not going to do that.

I then expected too, that perhaps expansion could collect the like powers. Well, it did, but the result was not further usable. It displays correctly but cannot be copied/pasted/edited/whatever. We cannot do anything more with that than... looking at it. Of course it is a big expectation to think that results put on history are further usable the normal way...

(10-06-2014 04:27 PM)parisse Wrote:  This is not my CAS versus other CAS, it's math.

You do not convince me as long as I see that other CAS tools on comparable hardware do what I/we want right out of the box. (Except of course if all the others are not CASs and Wolfram is some kind of Houdini-Club, in which case I will be only glad to buy non-CAS tools and to hire magicians!)

(10-06-2014 04:27 PM)parisse Wrote:  And by the way, Xcas has a fast kernel for polynomial/rational fraction computations (comparable to the best CAS).

Sorry, if it does not serve our needs, then it may also fly faster than light and lay golden eggs. It is still as useless to us as a Ferrari on the dirtway.

It is absolutely no option for us the way it is now. Perhaps some future update but not now.

Ciao,

Nick