HP 20s

[Mark Charles]

1. Does anyone know how to access the in built programs on the 20S?
2. What function does the INPUT key serve?

Just bought this calculator with no manual & require basic use
knowledge...

Thanks

Mark Charles

[Stefan Wolfrum]

Mark,

I have a 20S in my collection and have a manual, too.
Here are some info you might need:

The INPUT key:

This key is used for binary function to separate the first
from the second argument or in two-dimensional statistical
operations.
Example 1:
1 INPUT 1 ->P
This converts the rectangular coordinates (1,1) to Polar coordinates
(45 degrees, SQRT(2)).
In the display you get the 45 first. Press SWAP to get the 1.4142...

The number of possible 2-element sets out of a 4-element set can
be calculated as follows:
4 INPUT 2 Cn,r

Built-in program library:

There are six program built in:
A: root (root finder),
B: int (numerical integration),
C: CPL (operations on complex numbers),
D: 3 bY 3 (3x3 matrix operations),
E: qUAd (solving quadratic equations),
F: Fit (curve fitting).

These programs are copied into the program memory of the
20S if you recall them from ROM. So your own program will be
lost!
You access the programs via the LOAD key. For example press
PRGM LOAD A to load the root finding program. You can scroll
through the program now by pressing the blue up/down arrow keys.

To use these tools you have to modify the program and insert
the formula to be integrated or the equation whose roots have
to be found at the end of the loaded program. (This applies for
programs A and B). If you need more info here, mail me.

Programs C to F don't need a modification.

For complex operations use PRGM LOAD C PRGM and then:

- for addition (a1+b1i)+(a2+b2i): a1 INPUT b1 XEQ A a2 INPUT b2 R/S
- for subtraction ...: a1 INPUT b1 XEQ B a2 INPUT b2 R/S
- multiplication: a1 INPUT b1 XEQ C a2 INPUT b2 R/S
- division: a1 INPUT b1 XEQ D a2 INPUT b2 R/S
- inversion 1/(a+bi): a INPUT b XEQ E
- exponentiation (a+bi)^n: a INPUT b XEQ F n R/S
- absolute value SQRT(a^2+b^2): a INPUT b XEQ 9

3x3 matrix operations:
Given

a11 x1 + a12 x2 + a13 x3 = b1
a21 x1 + a22 x2 + a23 x3 = b2
a31 x1 + a32 x2 + a33 x3 = b3

program D solves the system for x and calculates the determinant
of the matrix and can be used to calculate the elements of the inverse
matrix.
Store the aij as follows into the registers:
R7: a11 R8: a12 R9: a13
R4: a21 R5: a22 R6: a23
R1: a31 R2: a32 R3: a33

Then store b1 in R0, enter b2, press INPUT, enter b3 and press XEQ A.
Now you should see x1. Press R/S to get x2 and R/S again to get x3.

To get the determinant press XEQ D.

To get the inverse matrix, solve for b=(1,0,0), b=(0,1,0) and b=(0,0,1) to
get the first, second and third column of the inverse matrix, respectively.

Solve quadratic equations ax^2+bx+c=0:

PRGM LOAD E PRGM.
Enter a, XEQ A, b XEQ B, c XEQ C.
Press XEQ D to solve for x.
If the indicator : is not visible the shown number is the first real root.
Press R/S to get the second real root.

If you see the indicator : the shown number is the imaginary part
of the complex root. Press SWAP the get the real part. The second
complex root is the complex conjugate of the first.

The use of program F is somewhat more complicated. Mail me if
you need instructions here.

Hope this helps,
Stefan.