Variables don't transfer to equations

[twolowiec]

No idea why this doesn't work.

Even though this works as intended:

So it works for substituting B1 for D1 and F1 just fine, but for some reason substituting B1 for whatever it is defined doesn't work.

Thanks in advance.

[RichardJ]

It's hard to debug a picture. Please post your worksheet (click on "Use Advanced Editor" at the top right of the edit dialogue).

[vlehner · Accepted solution]

Hi Thomas,

to get a symbolic result by given B1, you must recall the Function D1.

if you define B1 as "global Definition" you don't need to recal D1:

Best Regards, Volker

[twolowiec]

Thank you! That works perfectly. I'm coming from Mathematica, so I'm still not clear on how things work.

[Werner_E]

> to get a symbolic result by given B1, you must recall the Function D1.

In other word - define D1 AFTER you assign B1 a value.

Another option would be to turn D1 into a function of B1 as shown below.

A third options is a redefinition of just D1 (not the whole defining expression) combined with symbolic eval (see below)

Nevertheless the substitute, b12=1 command should work, but it doesn't.

A little bit strange anyway.

[Werner_E]

Indeed some strange effects. Guess we can call it a bug in the symbolics!?

[vlehner]

Werner Exinger schrieb:

Indeed some strange effects. Guess we can call it a bug in the symbolics!?

No Werner, it isn't.

It's the kind of definition variables.

Gruß, Volker

[Werner_E]

Guess no.

If an expression (no matter if typed in or stored in a variable) is evaluated symbolically using the substitute command, this command has to work as it should. The different handling of an expression stored in a variable and an expression typed in manually is not as it should be (while it may be explainable by the way a symbolic expression is stored internally).

[vlehner]

you're right, the "substitute" Command should work in any case, but i tryed and it works. Strange situation.

[Werner_E]

> you're right, the "substitute" Command should work in any case, but i tryed and it works. Strange situation.

thats even crazier!

It works for you because you had not defined B1 at worksheet level. If you define B1 before the symbolic eval with substitute, it does not work.

We may call it an unexpected or undesired behavior or we may call it a bug.

[vlehner]

What MC Version do you use?

I am using MP4.

[Werner_E]

> What MC Version do you use

That depends. Sometimes 3.0, sometimes 3.1- I did not find it necessary to fire up 4.0on any of the machines I am working on. Prime is such a useless c r a p !

And I am stilll on some XP machines where 4.0 would not install at all, I think.

I have just installed Prime to ensure that I don't miss anything if i don't switch.

Guess I won't switch ever - rather to a combi of Matlab and Maple - still in the learning phase and missing the whiteboard interface. Sometimes I even begin to like Geogebra - strrange.

[vlehner]

Hi Werner,

Prime is such a useless c r a p !

Completely Agreed!

Sometimes I'm working with MC15, because it's much better than Prime.

The diagramms of MC15 are very good-in Prime it lacks completely.

Mostly I'm working with Prime because of the thousands of documents i have in prime- No chance to convert to MC15. Poor world.

But what shalls, These points we are talking about are discussed a hundred times in community and nothing has changed up to now, it's like in politics.