logₓy

01122019, 09:09 PM
Post: #1




logₓy
hi all,
I had cause to work out log₂ of a number today, and was vaguely surprised that I couldn't find it on my calculators, not even as a function, let alone on a key. Nor the more general logₓy. The WP 34S is to be congratulated for having both on keys, but I can't find either even as a function on my DM42 or HP 50g. It's trivial to write my own fn for e.g LOGy(x) (e.g. LOG SWAP LOG ÷), but am I missing something? Cambridge, UK 41CL 12/15C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 48GX 50g 35s 30b/WP34S Prime G2 & Casios, Rockwell 18R :) 

01122019, 09:12 PM
Post: #2




RE: logₓy
No, I think it is wanted. The log in different bases are not often used, compared to log_e and log_10 , therefore for other bases you are on your own.
you can contribute here: http://www.hpmuseum.org/forum/thread10271.html Wikis are great, Contribute :) 

01122019, 09:45 PM
Post: #3




RE: logₓy
thanks; I've added a comment to that thread.
Cambridge, UK 41CL 12/15C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 48GX 50g 35s 30b/WP34S Prime G2 & Casios, Rockwell 18R :) 

01122019, 10:42 PM
Post: #4




RE: logₓy
I was having the opposite problem the other day trying to (somewhat quickly) take the log_10 of some number on a Casio fx991EX, but the button I was using required an argument for the base and I thought it strange there'd be a button for that but not one for log_10. I did ultimately find it as a shifted function on the () key. At the time I thought it interesting that logₓy had its own button but log_10 didn't.


01122019, 10:49 PM
Post: #5




RE: logₓy
.
Hi, (01122019 09:09 PM)cdmackay Wrote: I had cause to work out log₂ of a number today, and was vaguely surprised that I couldn't find it on my calculators, not even as a function, let alone on a key. Nor the more general logₓy. The HP71B has several log functions (some in the mainframe and some in various ROMs), including LOG2(X) which admittedly is very handy for all sort of programming tasks. I also think that the HP75 had a general Log to any base, not sure if in the mainframa or perhaps in some ROM or other. V. Find All My HPrelated Materials here: Valentin Albillo's HP Collection 

01132019, 12:01 AM
Post: #6




RE: logₓy
thanks both,
(01122019 10:42 PM)Benjer Wrote: I was having the opposite problem the other day trying to (somewhat quickly) take the log_10 of some number on a Casio fx991EX, but the button I was using required an argument for the base and I thought it strange there'd be a button for that but not one for log_10. I did ultimately find it as a shifted function on the () key. At the time I thought it interesting that logₓy had its own button but log_10 didn't. yup, it's not even a shifted fn there, but the main key fn. (01122019 10:49 PM)Valentin Albillo Wrote: The HP71B has several log functions (some in the mainframe and some in various ROMs), including LOG2(X) which admittedly is very handy for all sort of programming tasks. I'll add one of those to my wishlist Cambridge, UK 41CL 12/15C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 48GX 50g 35s 30b/WP34S Prime G2 & Casios, Rockwell 18R :) 

01132019, 12:40 AM
Post: #7




RE: logₓy  
01132019, 01:29 AM
Post: #8




RE: logₓy
(01122019 10:49 PM)Valentin Albillo Wrote: I also think that the HP75 had a general Log to any base, not sure if in the mainframa or perhaps in some ROM or other. The HP75/71 mainframes include: LOG(X) Base e Log of X LOG10(X) Base 10 Log of X; 71B can also use LGT(X) The HP75/71 MATH ROMs include: LOG2(X) Base 2 Log of X LOGA(X,N) Base N Log of X (75 Only) The 71B also includes LOGP1(X) which is the value of Ln(1+x) So, pretty complete. Bob Prosperi 

01132019, 02:13 AM
Post: #9




RE: logₓy
rprosperi Wrote:The HP75/71 mainframes include: The HP71B also has LN(X) as an alternate spelling. Quote:The 71B also includes LOGP1(X) which is the value of Ln(1+x) Yes, in the HP71B you have in all six log possibilities, namely LN, LOG, LOG10, LOG2, LOGP1, LGT and if you fancy log to any base you simply define: 10 DEF FNL(X,N)=LN(X)/LN(N) and then you can use FNL(X,N) as part of any expression in a program, from the command line or in (urg!) CALC mode. Also, creating a new assemblylanguage keyword LOGA(X,N) in a LEX file is utterly trivial and would take just a few bytes. V. . Find All My HPrelated Materials here: Valentin Albillo's HP Collection 

01132019, 03:19 AM
Post: #10




RE: logₓy
(01132019 12:40 AM)Gerson W. Barbosa Wrote:(01122019 09:09 PM)cdmackay Wrote: It's trivial to write my own fn for e.g LOGy(x) (e.g. LOG SWAP LOG ÷), but am I missing something? nice. I think I'd just have put in an extra SWAP, but yours is more elegant. Cambridge, UK 41CL 12/15C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 48GX 50g 35s 30b/WP34S Prime G2 & Casios, Rockwell 18R :) 

01132019, 08:47 AM
Post: #11




RE: logₓy  
01132019, 09:11 AM
(This post was last modified: 01132019 10:01 AM by pier4r.)
Post: #12




RE: logₓy
(01132019 01:29 AM)rprosperi Wrote: The HP75/71 mainframes include: why is the 75/71 a mainframe? were those not pocket computers? edit: ah, maybe you mean the basic library without expansion cards. Wikis are great, Contribute :) 

01132019, 09:49 AM
Post: #13




RE: logₓy  
01132019, 09:58 AM
(This post was last modified: 01132019 03:29 PM by StephenG1CMZ.)
Post: #14




RE: logₓy
A pocket computer has a mainframe?
Like Dr Who's Tardis, I guess  it's bigger on the inside. It doesn't help that the forums on this site combine calculators and computers, so it's not immediately obvious unless you remember all the model numbers. Stephen Lewkowicz (G1CMZ) 

01132019, 10:28 AM
Post: #15




RE:logᵧx
(01132019 12:40 AM)Gerson W. Barbosa Wrote: LOGx(y) sounds more natural to me: We write \(\log_b(x)\) and Mathematica uses: Quote:Log[b,z] Thus my intuition is to use: log_{y}(x) Exactly as you suggested. (01132019 08:47 AM)Dieter Wrote: Yes, and I'm glad it is defined this way on the WP34s. No, it's sad it is defined this way on the WP34s. Cheers Thomas 

01132019, 11:07 AM
Post: #16




RE: logₓy
All of the programming languages I used that have log to a specified base, put the base second. I.e. log(x, b).
The 34S did originally calculate log_{x}y, but we changed the arguments around. I have a vague memory that this was to be consistent with y^{x}, but I could be wrong. Pauli 

01132019, 12:56 PM
Post: #17




RE: logₓy
(01132019 11:07 AM)Paul Dale Wrote: All of the programming languages I used that have log to a specified base, put the base second. I.e. log(x, b). ?!? – all 34s versions I ever used calculate log_{x}y. That's also what is shown on the emulator skins. I remember well the discussion about the argument order. My point is that you usually have a number in X and then you want to calculate the basexlog of it. For a base5log you now simply enter 5 [log_{x}y]. Just as you do it with powers: 5 [y^{x}]. 5 [ENTER] 3 [y^{x}] =>125 5 [log_{x}y] => 3 So this is similar to he mentioned log(x, b) function in the programming languages: enter x first, then the base. It's only that in RPN the xvalue happens to end up in Y and the base b in X. ;) Dieter 

01132019, 07:40 PM
Post: #18




RE: logₓy
I apologise to those who prefer the other ordering/labelling
I don't think I gave it much thought, but my naive thinking involved seeing e.g. log₂ as the function, and I normally use x to denote the input of f(), leaving y as the base. but I quite see the alternative, especially when you consider it as a function with two arguments, which of course it is. thanks! PS and I would normally write xtothey, but it's often ytothex on calculators. Cambridge, UK 41CL 12/15C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 48GX 50g 35s 30b/WP34S Prime G2 & Casios, Rockwell 18R :) 

01142019, 03:57 PM
Post: #19




RE: logₓy
(01132019 11:07 AM)Paul Dale Wrote: All of the programming languages I used that have log to a specified base, put the base second. I.e. log(x, b). FWIW, and adding insult to injury, the SandMath has LOGYX where Y denotes the base and X the argument  blame it to the reverse part of RPN ;) 

01152019, 06:07 PM
Post: #20




RE: logₓy
In the interests of fairness, I'm pleased to note that the Prime has both a key for logb (the 'C' key's collection of fillin examples), and a LOG(x, b) function [CAS logb(x, b)].
Cambridge, UK 41CL 12/15C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 48GX 50g 35s 30b/WP34S Prime G2 & Casios, Rockwell 18R :) 

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