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The mail
One day, surfing the digital waves of the web I found an Nspire program that could plot slope-fields and solutions to differential equations on the Nspire, which was not part of the pre installed functionality at that time. I looked at the program and thought I could add some improvements , so I contacted the original author, Philippe Fortin and asked if it was OK if I published my version. He answered me and said it was strange that I even had seen this, since it was part of something he, and others, where writing for TI.
Later on I got an Email from someone at TI (I don’t remember the name right now) who asked me if it was Ok if TI bundled the version with my contribution added, with the next software update, and I said it was Ok.
In the end the software was truly an internation work. This text of the the last page of the document states:
| This document is based on contributions by Philippe Fortin (France), Mauritz Blomqvist (Sweden), John Hanna (USA), Doug Lapp (USA), Jon Roberts (Australia) and Steve Arnold (Australia). |
My contribution was to make it behave gracefully when reaching slopes near infinity, and also to enable it to “loop around” if one so wishes.
This is did by a rather neat trick if I may say so. When the slope was outside the range ±1 the program switch the viewpoint, it started to treat x as the dependent variable and y as the independent. That meant that, as it traversed the curve, the slope was always small, which improved the accuracy, but also that the problematic situation with an infinite slope now had turns to the gentle situation with a slope of 0.
The program: Differential Equation Plots
Texas instrument
The contact I now had established with Texas instrument meant that I have done other works for them (but paid ones now). Mainly as a T3 teacher. I have also worked for the publisher Natur & Kultur, mainly writing Lua programs, and this also because of the contacts I have got with Texas instruments.
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