Casio fx-3600PV/PA root finder

[Dave Britten]

I received a Casio fx-3600PA in the mail today, and it's definitely one the weakest scientific programmable calculators I own. 38 steps of program memory, 7 storage registers, and barely any flow control. Thanks to its two separate program areas, I was at least able to implement a simple root finder using the secant method, though it does require a certain amount of manual iteration control.

You'll need to do some extra prep when entering the program so that you don't run into a division-by-zero error while entering the steps - this model actually performs the calculations as the steps are being recorded! Just do all of the setup steps and program steps from top to bottom to get the program entered into program area P2.

Code:

Setup steps:
MODE EXP
1
Kin 3
Kin 4
2
Kin 5
P2

Program steps:
Kin 6
Kout 5
-
Kout 6
*
(
Kout 3
-
Kout 5
Kin 3
)
÷
(
Kout 4
-
Kout 6
Kin 4
)
=
Kin 5

This will leave you with 18 program steps to implement your function in P1.

Here's an example: -2x^2+13x-3

Code:

MODE EXP
P1

Min
x^2
*
2
+/-
+
1
3
*
MR
-
3
=

With P1 computing f(x), use this procedure to find the value of x such that f(x)=0:

1. Enter Guess 1
2. Kin 3, P1, Kin 4
3. Enter Guess 2
4. Kin 5, P1
5. P2 (next x value will be displayed)
6. P1 (next f(x) value will be displayed)
7. If display value is not equal to zero, repeat from step 5
8. Kout 5 to recall value of x

If you try the example above using 0 and 1 for initial guesses, you should arrive at x=0.239601355 after a few iterations.

Note: if the value of f(x) converges sufficiently close to zero, performing step 5 may cause a division-by-zero error due to the last two values of x being equal. If this happens, pres AC and Kout 5 to recall the last value of x. This can be seen if you try the example with initial guesses of 10 and 11, arriving at x=6.260398645.