# TACS: An Analog Computer Emulation - A Propeller/ Tachyon Application

nchlor
Posts:

**11**Can you solve differential equations on a propeller. Yes you can , using an analog computer emulation.

The displayed figure shows the chaotic solution to the Lorenz attractor. This post is an update of a previous post many years ago. It consists of two documents: a manual which details the TACS language & hardware, as well as several examples showing the range of application.

Since I wanted to include all features of hybrid-analog computers in my emulation, which required more memory than available in the P1, I used a FPGA P1 with 64K ram. A reduced form of the program will run on the P1. My intention is to transfer the program to the P2 where ram is not a problem.

## Comments

51very cool. And you do this all from the display? So you enter the equation on the display and it plots the solutions for say z, zd/dt, and zd2/dt2?

I do time dependent simulations with ACSL (no longer available) and MATLAB software. We use the Euler because we run a small time step and it is pretty straight forward. I haven't heard of the TRAPZ before. The ACSL simulation software has options to do other options like Adams-Moulton (variable), Gear's Stiff (variable), Runge-Kutta (fixed), Runge-Kutta-Fehlberg (variable), Adams-Bashforth (fixed), ODEPACK (variable), and CVODE (variable). I've been wanting to learn more about those but have not yet, will add Trapz to the list.

11Ludis:

I have found the Euler integrator to give reasonable results. TACS is a command driven system. You must connect to a terminal emulation ( eg, Terra Term) to access the program. The differential equations are transformed into a series of connected blocks. See the Van der Pol equation example. The model VDPOL is emulation of an analog computer patch panel. Compare this example with the template on the first page.

The display is used to show the the graphic solutions to the selected model. All commands are entered in the terminal.

I have used Mathematica + System Modeler to verify my TACS results.