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24-Ruby III

## Bug in symbolic Math?

I see one very strange bug!

I have had solved a system of 2 algebraic equation - not correct solution!

I have simplified its - correct solution!

11 REPLIES 11
23-Emerald III
(To:ValeryOchkov)

No worksheet, no picture... do you want us to guess?

Luc

24-Ruby III
(To:LucMeekes)

I am preparing the example.

Now you can translate and read one old joke!

Приходит пьянный студент в свою комнату в общаге, садиться на кровать, снимает один ботинок и со всего размаху бросает его в стенку.

Тут раздается крик из-за стенки:
— Ты идиот - 3 часа ночи, а ты спать не даешь!!!
Тогда студент тихо снимает второй ботинок и ложится спать.

Через два часа истошный крик соседней комнаты:
— Я долго буду ждать, когда ты второй ботинок снимешь???

13-Aquamarine
(To:ValeryOchkov)

Viktor
24-Ruby III
(To:ViktorKorobov)

Thanks, Viktor!

One good example.

One more Symbol Math bug here

Nautilus

24-Ruby V
(To:ViktorKorobov)

Mathcad (resp. muPad) defaults to working in the complex  plane where e.g. the logarithm is not unique and the rules we are used from the reals space do not apply in the same way.

So I guess we don't see a bug here.

If we tell Mathcad/muPad that we would like to stay in reals space (meaning the log arguments are all positive reals) does the trick

I guess what we see in your example is not a bug but rather the result of a very cautious behavior of a mediocre symbolic engine. MuPad is not aware in the first step that the equation ln(9-y)-ln(y)=ln(2) has no other (not even non-real) solutions but y=3.

If we ask Mupad for the solutions of this equation explicitly it seems to realize that 3 is the only solution.

Alas, we know that muPad is not the symbolic engine we would like to see to work under the hood of Mathcad. And i see no plans that PTC would like to change over to a better symbolics, rather the change is that Mathcad itself is losing quality in a catastrophic way, so the mediocre Symbolic may be the considered best part of it.

13-Aquamarine
(To:Werner_E)

Viktor
24-Ruby V
(To:ViktorKorobov)

@ViktorKorobov wrote:

I strongly second that - thanks to Maple symbolics still the best Mathcad ever. But times flies and things got even worse - look at Prime. Guess we have to realize and admit that we have reached the end of Mathcad as we knew it and have to move on to other software. Sad story.

24-Ruby III
(To:LucMeekes)

@LucMeekes wrote:

No worksheet, no picture... do you want us to guess?

Luc

Sorry! I have check in one more! Is it a bug or...?

24-Ruby V
(To:ValeryOchkov)

No bug!

Looks like you forgot to highlight the minus sign in front of the fraction when you copied the expression of the unsimplified result. So the sign is wrong and thats the reason for the supposed discrepancy.

24-Ruby III
(To:Werner_E)

@Werner_E wrote:

No bug!

Looks like you forgot to highlight the minus sign .

Opppps!

И на старуху бывает проруха!

21-Topaz II
(To:ValeryOchkov)

Selling shoddy products is a deliberate and malicious action otherwise it would be like .... "throw pearls to pigs" .... Quality costs a lot and isn't for everyone.........

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