HP 42S undocumented [MAX] [MIN] functions

[pchilderhose]

I am attempting to type in a program and utilizes an undocumented [MAX] or [MIN] function. The problem I am encountering is that I cannot find that function in my calculator. I was wondering if anyone know how to access this function when programming an HP 42S calculator.

[rprosperi]

(10-29-2022 07:11 PM)pchilderhose Wrote:  I am attempting to type in a program and utilizes an undocumented [MAX] or [MIN] function. The problem I am encountering is that I cannot find that function in my calculator. I was wondering if anyone know how to access this function when programming an HP 42S calculator.

Try using [XEQ] which can be used to run any function, you do not need to select functions from a menu.

[XEQ] "MAX"
[XEQ] "MIN"
[XEQ] "AnyFucntion"

[lrdheat]

I am not aware of such functions (would love to find that they are there). Here is a work around (will not work with Nroots involving negative numbers):

LBL “DX”
MVAR X
MVAR H
RCL X
RCL H
COMPLEX
XEQ “FX”
COMPLEX
RTN
END

H (epsilon) of 1E-5 works well

FX is your program of the equation f(x) that you wish to find an extremum.

Finding an extremum consists of solving DX, then executing FX with the number that solving DX placed in the x level of the 4 level stack.

[lrdheat]

…of course, it helps to have an idea of what range of values to use in the solve program, but the solve is pretty good at finding candidate solutions, even if you do not have an idea!

[Guenter Schink]

(10-29-2022 07:11 PM)pchilderhose Wrote:  I am attempting to type in a program and utilizes an undocumented [MAX] or [MIN] function. The problem I am encountering is that I cannot find that function in my calculator. I was wondering if anyone know how to access this function when programming an HP 42S calculator.

The undocumented [MAX] and [MIN] are not accessible through any menu on the HP42S. You have to type in them manually. The brackets are part of the command, i.e. you have to type in not only "MAX" but in fact "[MAX]".

Günter

PS: they are available on Free42 at the end of the "Catalog" "FCN"
For explanation look here

[lrdheat]

Do I understand that these commands only work in the MATRIX application as opposed to finding a max or min of a function of interest?

[rprosperi]

(10-29-2022 10:00 PM)Guenter Schink Wrote:  The undocumented [MAX] and [MIN] are not accessible through any menu on the HP42S. You have to type in them manually. The brackets are part of the command, i.e. you have to type in not only "MAX" but in fact "[MAX]".

Thanks Günter for correcting my sloppy reply, omitting the brackets.

The hidden functions in the HP-42S are documented here, by Joe Horn, who discovered them (waay back in the day):

https://www.hpmuseum.org/forum/thread-8887.html

[pchilderhose]

I contacted Joseph Horn directly.

He told me how to input the [MIN] [MAX] etc.

Press the XEQ key
Use the Alpha keys to input [MIN]
Press ENTER when complete

The result is:
06 [MIN]

If you just use the Alpha keys you get:
06 "[MIN]"

(Keep in mind that "06" is an arbitrary line number in a program being entered)

Later in the program I encountered 1E-11

I don't use my 42S for much anymore, but still love it, so I was unsure how to input this line of the code. It is entered below
Press the E key beside the +/- key
Press the +/- key
Press the 1 key
Press the 1 key
Press the Enter key

The result is:
07 1E-11

(Keep in mind that "07" is the next arbitrary line number in a program being entered)


Thank you all for responding to my question.