Absolute value: sometimes CAS is very clever, sometimes not!

[compsystems]

(09-08-2018 06:05 AM)parisse Wrote:  If you want to play with evaluation, make sure that Simplification is set to None in CAS Settings.
Then a:=domain(1/(x+1),x); followed by eval(a,1) will return x!=-1.

ok, but please hppteam include for next firmware the xcas autosimplify() command , otherwise how do I change the flag from a program code? if I need some times, maximum simplification and other times, do not simplify

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(09-08-2018 10:43 AM)ijabbott Wrote:  Back to compsystem's point, why does 'x ≠ -1' get simplified to a boolean 'true' if x is unknown?

(09-08-2018 10:52 AM)parisse Wrote:  Because x (identifier) is different from 1 (integer), like for == which does not mean "mathematically equivalent".

And with what purpose the operadopr = acts as ==, if there is a command (==) or evalb() for that purpose, also for ≠

PHP Code:

evalb(x ≠ -1) returns True
evalb(1 = 2) returns False
evalb([x<>1, equal(1,2)] ) returns [True,False] 


I think that the operator =, ≠, should not operate as a comparator, this affects the logic of the algorithms, so I suggest a cas flag for these operators do not assume the comparison.

Another option is for the system to ask what kind of data it is . If it is symbolic assume(x,symbol);, do not compare