Monthly Archives: May 2015

Exponential smoothing in Nspire

This is a program for exponential smoothing, originally for the TI-89 Titanium as published in the Advanced Placement Statistics with the TI-89. The plotting functions for TI-89 are not plotted but it is easy to obtain a similar plot in the Nspire. Below is the DJIA example in the original text, Topic 43.

exsmooth

ARIMA ACF/PACF Correlogram in Nspire

During the identification phase of the Box-Jenkins models, a correlogram charting the ACF and PACF are useful. The color screen of the TI Nspire is perfect to visualize the output from the program calculating these values. Here is the classical plot on the example airline passenger data from the original time series analysis text: Time Series Analysis: Forecasting and Control.

arima-acf

Solver behaviour on HP Prime, 50g, 39gII, TI Nspire CX CAS, and Casio fx-9860GII

On comparing the differences in behavior of TVM calculations, the solver of HP Prime is the only calculator able to return, without any initial guess input, the approximate value of number of period in a peculiar form of future value finding equation, although with not small of an error of about 13%.

Edit: Added results from 50g and 39gII emulator, they both returned the same result (but not the same as the Prime) without being given any hints.

HP Prime:
penny-prime

HP 50g
penny-hp50g

HP39gII
penny-hp39giipenny-hp39gii2

TI Nspire: penny-nspire2

Casio fx-9860GII:
penny-casio1 penny-casio2

The original problem is from an classic HP calculator manual published in 1982. The problem goes like this (example 2 on page 145): If an employee is paid $0.01 every second, with an interest rate of 11.25% compounded every second, what will she get after a year? In the original document, this problem is used to illustrate the limitations numerical accuracy. Detailed explanation and workarounds can be found in the original document.

Improvised semi-automatic timer to record long running Nspire calculations

In recent calculator overclocking tournaments, some programs took over more than a few minutes to finish. In extreme cases, programs run over an hour. The size of data set of these long running calculations are not realistic in most cases for hand held calculators, but for the sake of overclocking comparison, they are attempted to obtain the time required.

Instead of just watching and waiting the calculator prompt to return and stop the stopwatch, a makeshift timing device is developed with an aim to automatically record the benchmark calculation run time on the TI Nspire. The device is simple and make use of the following components:

This device works in the following way:

  • The back-light of the Nspire will be on for the whole period running the benchmark calculation.
  • When the program is finished, the back-light will turn off after a predefined period, which is a user configurable setting.
  • An LED will act as an light sensing diode, and is placed on top of the Nspire screen. The voltage will be measured by the LaunchPad, and send periodically through the 703N router to Exosite.
  • From repeated testing the difference in voltage when the back-light is on and off are determined. This make it possible to set an alarm on Exosite with that known threshold.
  • The time to start the calculation is recorded manually. After starting, the task of taking the finish time will be taken care of by the Exosite alarm timestamp, as triggered by the drop in voltage detected from the turning off of the back-light.

lighttimer4

Best result of the LED threshold is obtained when working in the evening and lights are turned off. Although the time taken is not as accurate as taken manually by stopwatch due to the delay between measuring of consecutive LED voltage (set as around 4 seconds to avoid flooding Exosite), it should be good enough for long running calculations that span a quarter to more than an hour. Better methods for timing may exists (e.g. internal timers on the Nspire itself) but this improvised one with simple devices and a free cloud service worked quite well, for the best part is automation so that I no longer have to look out from time to time to check if the calculation is finished.

Overclock Tournament Round 3

In previous rounds, Casio fx-9860GII with overclocking software Ftune2 won both rounds in a Nelder-Mead logistic curve fitting speed test, although TI Nspire CAS CX with Nover closed the gap on the second round after a little optimization on the language by declaring most variables local in scope.

In this installment, the comparison focus on the basic calculation rather than the programming environment. This simple integration equation is to be computed by both overclocked calculators:

nspire_vs_casio_sin_0_to_100_eq

Again, Casio with Ftune2 outperform the TI Nspire.nspire_vs_casio_sin_0_to_100