thread repost: Discussion on Parser/UI Options

[Manolo Sobrino]

(04-04-2014 12:06 PM)CR Haeger Wrote:  Hi Manolo

I believe your example for y:=x definition in CAS may have an error.

Only y appears to become a CAS variable after excecuting this so x is not defined. I'm not surprised at a HOME x throwing an error.

Carl

You're right. I was testing several possibilities before writing the post and my Vars menu got populated, maybe I defined x too or maybe it's a case of creeping dyslexia.

Tried it again after purging everything, only y appears as a CAS variable, everything works as I described before (that was what made me think about it in the first place). You can define explicitly x in CAS, and it still works that way. For instance, define (in CAS) x:=r, input x at HOME and it will print r. Now x and y appear in the Vars menu as CAS variables, r doesn't. If you input y you get x again... And if you define x:=1 in CAS, and switch to HOME it'll still print x when you input y. CAS can work with undefined variables, HOME needs defined variables as an input and will use just the definition for evaluation. It would be nice to take advantage of this, so that you could perform calculations involving any new variable without the need to define a dummy one first. Then you could go back and forth to CAS smoothly.

Or, more easily, you could just send your expression involving undefined variables to the CAS (that can handle them) by calling evalf(expression) and print the answer.