What does the HP20S function "yx" do???


I need to know what the "yx" (top roww of keys) do when you press it.
You enter a number = 89.25
divide it by 1.03510
press "yx" key
and then 4.85

and the result is 75.4995

What have I done with that key????



The function "yx" is y to the power of x. An easier example of y=2 and x=3 equals 2 x 2 x 2 = 8. So in your example 1.0351 yx 4.85 = 1.182127 and your first number of 89.25 divided by 1.182127 = 75.4995. Hope this helps. I wish I had the math background of most of the users of this forum to explain more eloquently.


As George explained below, yx is the power function, "y**x" in Fortran or "pow(y,x)" in C.

Of course, with the mathematical precedence in the "Algebraic" HP-20S, you calculated

89.25 / (1.035104.85) = 75.4995

Is that what you intended? For,

(89.25 / 1.03510)4.85 = 2,442,225,117.82

-- KS


Well, it seems the key should be xy not yx. I think this has been commented before.



I haven't seen the earlier discussion your refer to, but I think the reason for this "yx" order is the way we say the expression (at least in English.) For example, the expression m^n would be spoken as "m to the n power." The m is the first item mentioned, and then the exponent n.

Calculators are designed to accept the data in this same order, first the m value and then the n value. In an RPN machine, this means that the m gets pushed into the y location in the stack, with the power in x. Hence, yx is the reaonable way to label the key.

I, too, was a bit confused by this notation when I began using a calculator, but I finally saw the reasoning behind it and now perform this calculation without a second thought, simply keying the values in their"natural" order.

Hope this explanation is clear.



It was x^y on the HP-35. They switched it to y^x on the HP-80, HP's second pocket calculator. Looking at the old desktop RPN calculators, The HP-9100 didn't have x^y or y^x, a strange omission. The HP-9810A had x^y as an option. The HP-9815 had y^x. TI seems to have been consistent in using y^x on all of their early scientific calculators.


Y^X - read as "y to the xth power" may not seem intuitive but it truly is - on both HP and TI calculators. For discussion, we can refer to the 'y' value by its real name, 'base', and the 'x' value by its real name, 'exponent'.

In fact, the name has to be 'weird' to have the arguments entered in 'natural' order.

Real HP calcs have a 4-level stack (X,Y,Z, and T registers), and also a LastX register too. So to perform this calc we key in

&nbsp&nbsp [B]base[/B] [ENTER] [B]exponent[/B] [Y^X]

After ENTER is hit, the base value is lifted to the Y register, and the X register receives the exponent.

On TI/AOS calcs, Y^X works similarly but with infix, not postfix notation:

&nbsp&nbsp [B]base[/B] [Y^X] [B]exponent[/B] [=]

On these calcs, the 'held value' - the base - gets stored in a "y" register pending calculation. (That's why you'll also see an [x<>y] (exchange x with y) on many of these calcs.

Bill Wiese
San Jose


Thank you to all !!!!!

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