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From: Merciadri Luca on 10 Mar 2010 08:12
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Hi,

I was solving chemistry problems with my 50g, when I realized that
SOLVEX fails with an equation of the 2nd degree where products are not
indicated using dots.

For example, using RPN:

2:'x^2 + x(x-4) +3x'
1:SOLVEX

won't work, and will display an error message to explain that the
expression cannot be reduced to a canonical form. Is it normal?
I would accept this as a normal thing iff the 50g was using
parentheses to compute, say, <f, g>, where f and g are two functions,
but I do not think that it has this kind of capabilities.

Thanks.
- --
Merciadri Luca
See http://www.student.montefiore.ulg.ac.be/~merciadri/
- --

Life is like a box of chocolate, you never know what you're gonna
get.
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From: John H Meyers on 10 Mar 2010 09:52
On 3/10/2010 7:12 AM, Merciadri Luca wrote:

> For example, using RPN:
>
> 2:'X^2 + X(X-4) +3X'
> 1:SOLVEVX

The expression seems pretty hard to enter in RPN mode
(invalid syntax), but if entered in Algebraic mode,
with 'X' undefined, just one instance of 'X' is taken to mean
a user-defined function of argument (X-4), which later causes
Error: Not reducible to a rational expression

I.E. `X^2 + X(X-4) +3X` [note the back-quotes]
produces [at least with my flags], in SysRPL syntax:

SYMBOL ID X ZINT 4 x- SYMBOL ID X ; BINT1 xFCNAPPLY <== function!
ID X ZINT 2 x^ ZINT 3 ID X x* x+ x+ ;

As you correctly concluded,
X*(X-4) would be better RPN syntax than X(X-4)

I suppose there must be some "operator precedence" rule for ALG mode
that must dictate "function of" to be higher priority
than "implied multiplication" -- or is there?

[r->] [OFF]
From: Merciadri Luca on 10 Mar 2010 10:21
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John H Meyers <jhmeyers(a)nomail.invalid> writes:

>> For example, using RPN:
>>
>> 2:'X^2 + X(X-4) +3X'
>> 1:SOLVEVX
>
> The expression seems pretty hard to enter in RPN mode
> (invalid syntax), but if entered in Algebraic mode,
> with 'X' undefined, just one instance of 'X' is taken to mean
> a user-defined function of argument (X-4), which later causes
> Error: Not reducible to a rational expression
>
> I.E. `X^2 + X(X-4) +3X` [note the back-quotes]
> produces [at least with my flags], in SysRPL syntax:
>
> SYMBOL ID X ZINT 4 x- SYMBOL ID X ; BINT1 xFCNAPPLY <== function!
> ID X ZINT 2 x^ ZINT 3 ID X x* x+ x+ ;
>
> As you correctly concluded,
> X*(X-4) would be better RPN syntax than X(X-4)
>
> I suppose there must be some "operator precedence" rule for ALG mode
> that must dictate "function of" to be higher priority
> than "implied multiplication" -- or is there?
I totally agree with you. I wanted to write (actually somewhat
unofficial) `pseudocode' for my entries on my RPN stack. Furthermore,
I supposed that all the operations to form the element on level 2 had
alreadu been performed, thus resulting in the result I displayed for
level 2.

You do not seem to give a personal point of view about the `Not
reducible to a rational expression' error when one is working in
symbolic mode and wants to solve a symbolically-constituted equation
for the defined symbol. This error only happens, as I stated before,
when the user does not use `*' as a product operator in |R.

- --
Merciadri Luca
See http://www.student.montefiore.ulg.ac.be/~merciadri/
- --

Look on the sunny side of life.
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From: John H Meyers on 10 Mar 2010 10:53
On 3/10/2010 9:21 AM, Merciadri Luca wrote:

>>> 2:'X^2 + X(X-4) +3X'
>>> 1:SOLVEVX

> You do not seem to give a personal point of view about the `Not
> reducible to a rational expression' error when one is working in
> symbolic mode and wants to solve a symbolically-constituted equation
> for the defined symbol. This error only happens, as I stated before,
> when the user does not use `*' as a product operator in |R.

You had said RPN (mode?), and you can't even enter that in RPN mode
(nor can you omit multiplication operators anywhere in RPN mode).

In ALG mode, the expression compiles into something which has no meaning,
because one 'X' is a function which takes an argument,
and the remaining 'X' have no arguments -- there is no
"implied multiplication," because "function of (X-4)"
evidently took precedence, compiler-wise.

What does it mean to "solve" an algebraic expression (for a "zero")
if the expression itself has no meaning?

I'm satisfied just to not get a TTRM :)

--
From: Merciadri Luca on 10 Mar 2010 12:55
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John H Meyers <jhmeyers(a)nomail.invalid> writes:

> On 3/10/2010 9:21 AM, Merciadri Luca wrote:
>
>>>> 2:'X^2 + X(X-4) +3X'
>>>> 1:SOLVEVX
>
>> You do not seem to give a personal point of view about the `Not
>> reducible to a rational expression' error when one is working in
>> symbolic mode and wants to solve a symbolically-constituted equation
>> for the defined symbol. This error only happens, as I stated before,
>> when the user does not use `*' as a product operator in |R.
>
> You had said RPN (mode?), and you can't even enter that in RPN mode
> (nor can you omit multiplication operators anywhere in RPN mode).
>
> In ALG mode, the expression compiles into something which has no meaning,
> because one 'X' is a function which takes an argument,
> and the remaining 'X' have no arguments -- there is no
> "implied multiplication," because "function of (X-4)"
> evidently took precedence, compiler-wise.
>
> What does it mean to "solve" an algebraic expression (for a "zero")
> if the expression itself has no meaning?
Sorry, I thought I had already specified the `=0' part. What is
actually needed is to find roots of the parabola defined by the first
member I gave previously. Sorry for my incompetence in these
calculators, but I am just a normal user.

I now understand the problem. I had not sufficient knowledge in HP
calculators to think about this the way you did.

Thanks, John.

- --
Merciadri Luca
See http://www.student.montefiore.ulg.ac.be/~merciadri/
- --

Love is not finding someone to live with; it's finding someone whom
you can't live without.
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