50g prefers LN instead of LOG during symbolic solve
09-30-2014, 11:01 PM
Post: #1
 fire_for_effect Junior Member Posts: 6 Joined: Sep 2014
50g prefers LN instead of LOG during symbolic solve
The 50g seems to prefer the log natural instead of log 10 when symbolically solving "Y=2^X" . The result is "X=LN(Y)/LN(2)" which would be correct except I am looking for a base 10 solution ... any thoughts on flag changes or how to change solution behavior to get this solution: "X=LOG(Y)/LOG(2)" ?
10-02-2014, 03:09 PM
Post: #2
 Eddie W. Shore Senior Member Posts: 976 Joined: Dec 2013
RE: 50g prefers LN instead of LOG during symbolic solve
(09-30-2014 11:01 PM)fire_for_effect Wrote:  The 50g seems to prefer the log natural instead of log 10 when symbolically solving "Y=2^X" . The result is "X=LN(Y)/LN(2)" which would be correct except I am looking for a base 10 solution ... any thoughts on flag changes or how to change solution behavior to get this solution: "X=LOG(Y)/LOG(2)" ?

There is no flag that switches between LN and LOG. (Advanced User Reference)
10-02-2014, 04:23 PM
Post: #3
 Claudio L. Senior Member Posts: 1,610 Joined: Dec 2013
RE: 50g prefers LN instead of LOG during symbolic solve
(09-30-2014 11:01 PM)fire_for_effect Wrote:  The 50g seems to prefer the log natural instead of log 10 when symbolically solving "Y=2^X" . The result is "X=LN(Y)/LN(2)" which would be correct except I am looking for a base 10 solution ... any thoughts on flag changes or how to change solution behavior to get this solution: "X=LOG(Y)/LOG(2)" ?

As far as getting a numeric result, this is a base-2 logarithm, and that's what you get. I'm curious why do you need a base-10 solution (or any specific base for that matter), when it doesn't make any difference in the result. Just aesthetics or there's some other reason behind it?
10-02-2014, 04:29 PM
Post: #4
 fire_for_effect Junior Member Posts: 6 Joined: Sep 2014
RE: 50g prefers LN instead of LOG during symbolic solve
I believe I misspoke when writing my original question. I must have been really tired. I know its a base 2 solution. Well I was looking for was log and not LN .
10-03-2014, 01:44 PM
Post: #5
 Claudio L. Senior Member Posts: 1,610 Joined: Dec 2013
RE: 50g prefers LN instead of LOG during symbolic solve
(10-02-2014 04:29 PM)fire_for_effect Wrote:  I believe I misspoke when writing my original question. I must have been really tired. I know its a base 2 solution. Well I was looking for was log and not LN .

I think you were perfectly clear. You want the expression written in terms of the base-10 log() function instead of ln().
Let me put my question in perspective now: I'm developing a new firmware for the 50g, and it will include a new CAS from scratch. Your request seems doable, so it could potentially be implemented in our project. But I can't think of any practical reason why it's needed, hence my question to you since you seem to have that particular need.

Claudio
10-03-2014, 04:44 PM (This post was last modified: 10-03-2014 04:49 PM by C.Ret.)
Post: #6
 C.Ret Junior Member Posts: 17 Joined: Dec 2013
RE: 50g prefers LN instead of LOG during symbolic solve
HI,

In fact what is the difference between $$y=ln(x)/ln(2)$$, $$y=log(x)/log(2)$$ or $$y=Log(x)/Log(2)$$.
It really close to me prefered format: $$y=lg_2(x)$$
10-04-2014, 02:25 AM
Post: #7
 fire_for_effect Junior Member Posts: 6 Joined: Sep 2014
RE: 50g prefers LN instead of LOG during symbolic solve
well, even though the end result answer is the same, the numerical value of each individual symbol is not. Log(64) isn't the same as ln(64) , so inspection of each symbolic element isn't practical because the calculator is solving the problem differently than pen and paper solutions.
10-04-2014, 02:04 PM (This post was last modified: 10-04-2014 02:06 PM by C.Ret.)
Post: #8
 C.Ret Junior Member Posts: 17 Joined: Dec 2013
RE: 50g prefers LN instead of LOG during symbolic solve
Please note that even if the numerical value of $$ln\;64$$ differs from $$log\;64$$, the ratio $$\frac{ln\;64}{ln\;2}$$ and $$\frac{log\;64}{log\;2}$$ as well as $$lg_2(64)$$ are all identical to six.
10-04-2014, 02:20 PM
Post: #9
 fire_for_effect Junior Member Posts: 6 Joined: Sep 2014
RE: 50g prefers LN instead of LOG during symbolic solve
Yes I know... That's why I mentioned it. Is there really any reason for a symbolic solve on the calculator to favor ln in a solution? It can be non intuitive if you are looking for a textbook answer in terms of log. In That case, the answer would be graded wrong, even though the end result is the same, because each element is different than expected. I guess ultimately this is kind of a picayunish detail that can be compensated for in one's head.
10-04-2014, 04:20 PM
Post: #10
 Tim Wessman Senior Member Posts: 2,110 Joined: Dec 2013
RE: 50g prefers LN instead of LOG during symbolic solve
The problem is deeper then this.

In most/all calculators, LN has been used for base e logs, while log has meant base 10. However, in most/all symbolic packages, log means natural log and many don't even have a base 10 as a separate thing. This makes it quite difficult to merge numeric/symbolic ways of doing things.

Hence the reason why the 50g CAS (and pretty much all others) basically only work with LN. To them, there really isn't anything useful in anything *except* natural log.

TW

Although I work for the HP calculator group, the views and opinions I post here are my own.
10-06-2014, 01:30 AM
Post: #11
 fire_for_effect Junior Member Posts: 6 Joined: Sep 2014
RE: 50g prefers LN instead of LOG during symbolic solve
after doing a survey of multiple mathematic programs on the PC, I agree with Tim on the basis that even though the programs will show log they are in fact referring to LN. So I suppose I can chalk the rest of it up to naivety since I haven't used cas systems much before this and the confounding way that Microsoft's mathematics program ( free, btw) refers to ln as log.
10-06-2014, 09:06 PM
Post: #12
 Thomas Klemm Senior Member Posts: 1,448 Joined: Dec 2013
RE: 50g prefers LN instead of LOG during symbolic solve
(10-06-2014 01:30 AM)fire_for_effect Wrote:  though the programs will show log they are in fact referring to LN

In mathematics the function log refers generally to the natural logarithm.

Cheers
Thomas
10-26-2014, 09:31 PM (This post was last modified: 10-28-2014 11:58 PM by Gilles.)
Post: #13
 Gilles Member Posts: 162 Joined: Oct 2014
RE: 50g prefers LN instead of LOG during symbolic solve
(09-30-2014 11:01 PM)fire_for_effect Wrote:  The 50g seems to prefer the log natural instead of log 10 when symbolically solving "Y=2^X" . The result is "X=LN(Y)/LN(2)" which would be correct except I am looking for a base 10 solution ... any thoughts on flag changes or how to change solution behavior to get this solution: "X=LOG(Y)/LOG(2)" ?

HI ,

You can't change the LN preference of the 50G, but you can easily write a small program to convert any algebraic expression from LN (natural log) to LOG (decimal log)

\->LOG :
\<< {'LN(&A)' 'LOG(&A)*LN(10)' } \|^MATCH DROP EVAL \>>

Nota : \|^ is the up arrow

Please test this before use for serious purpose...
You can of course affect this to a user key if needed.

'Y=2^X'
SOLVEVX
\->LOG
and you get 'X=LOG(Y)/LOG(2)'

'Y=Z+10^X'
SOLVEX
\->LOG
and you get 'X=LOG(Y-Z)'

Gilles
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