MacResearch

In 'Showcase' reviews, the reviewer is the developer. No claim of objectivity is made, but it’s a chance for the developer to show off his/her app. Here, software developer Pierre-Henri Jondot talks about his plotting/graphing application TouchPlot for iPhone and iPod touch.

Just a note. The developer has posted that there is a new version of touchplot out (Version 4.0) and he's created a Youtube channel to show some of the features.

TouchPlot is a grapher application for the iPhone and iPod touch, which can be bought at the appstore since late july. As the developer of TouchPlot, my intention in this review is to give an idea of what can be done with TouchPlot, as well as to explain some of the design decisions I've made while developing this application.

When I decided that I wanted to give the iPhone SDK a try, the idea to write a grapher came easily, as I had developed a couple of months earlier a simple plotting framework for cocoa development, and its almost exclusive use of Quartz-2d primitives made it an excellent candidate for a port to the little device... It didn't take much time to have a glimpse on the simulator of what the iPhone might be capable of, so I applied to the developer program in the early summer, hoping to get accepted soon, which I did a couple of weeks later...

Working double-shifts, I managed to submit TouchPlot 1.0 on the 24th of july, to be sold at the price of 4.99$, and it got accepted and in the appstore before the end of the said month. It was the first grapher on the appstore, soon followed by many others... The work on TouchPlot did not end there, and many weeks of very sustained development and subsequent releases later, the actual version (as of 3/1/2009) of TouchPlot is 3.3 and an upgrade (bug fixes) has been submitted lately.

TouchPlot was made a staff favourite in many stores (including the US Store) in september, when TouchPlot 3.0 appeared and reappeared as a staff favourite quite recently (december 2008), but on three stores only : the French, the German and the UK ones (AFAIK). As of 3/1/2009, TouchPlot received 70 reviews on the Appstore, with an average of 4.29 stars.

The features of TouchPlot are too numerous to make an exhaustive list here. Of course it allows to plot several functions (up to four, f, f', g and h) with unequaled (so far) accuracy :

Parametric curves in polar or cartesian coordinates :

Differential equations (first and second order) solutions plotting, with a vector field (when it makes sense) :

Equations and inequalities solutions, with gradient field, as well as a 3d view of surfaces with equations z=F(x,y) :

One of the features I am the proudest of is the ability to include some parameters (a,b,c,d) in functions, equations, to add sliders to the graphing canvas and adjust the values of the parameters with the sliders, recalculating and redrawing everything in real time. It allows one to experiment the dependence on a parameter for a function, dependence on the initial term of a recurrent sequence :

Now the strongest point of TouchPlot might be its weakest at the same time : the formula editor...

The touchscreen of the iPhone and iPod touch is perfect to explore a graph, move around, zoom in and out, look for particular points (zeros, extrema), but the lack of a physical keyboard to enter a formula motivated me to look for new methods of compositing a formula. I got the idea of using direct Polish notation and it came out as a good choice for several reasons :
- it minimizes the number of needed keys (very important)
- it makes possible to format and display the formula being edited in a nice way (prettyprint), while making it impossible to obtain a syntax error
- it compels the user to think and analyse the formula while entering it, and the teacher I am is convinced this is a quality much more than it is a drawback...

Direct Polish notation is known as prefix notation too, which means operators are entered before their arguments. Something like exp(x+1)+x would be obtained with, in that order : +,exp,+,x,1,x

To my greatest surprise, the feedback I received early on was very positive, while I feared to receive bad critics for the choices I made (of course I did advertise them, and put many tutorials on the TouchPlot website...) Some bad critics came later, and a few were quite justified :
- the strict direct Polish notation TouchPlot used was cumbersome for some expressions, such as polynomials (doing +,*,a,^,x,2,+,*,b,x,c in order to get a*x^2+b*x+c was quite a pain, even for me)
- correcting a formula while editing was restricted to delete the last entered item... which meant retyping the full formula when someone forgot something at the beginning of it

It took several revisions of TouchPlot to adress the critics by reshaping the formula editor to what it is today, and I think it is now a very good compromise. Entering a polynomial such as a*x^2+b*x+c is just : a,x,^,2,+,b,x,+,c while the strict direct Polish notation can still be used. (In fact, for many little things, using Polish notation is encouraged, but when it becomes a bit too cumbersome, there are alternatives...)

A graphic designer (Toffenut design) worked with me on redesigned custom keyboards, and this is what the formula editor looks like now :

I think the keys are the right size for comfortable editing. It is now possible to select a part of the formula, delete it or append it, and, since version 3.3, one can now save formulas so as to constitute libraries of functions.

Note that if you are curious to try TouchPlot, I urge you to download its free counterpart, named TouchPlotLite, where you can try every feature of TouchPlot.
- Libraries for functions, parametric curves, differential equations are populated with examples so that you can load function examples, plot them and experiment
- The difference with the full-version is that only h function and polar curve definitions are editable, and the functions and equations libraries are read-only, but it will be enough for you to see if you can get used to the formula editor of TouchPlot and if you might have an use for TouchPlot or not...

Follow this link to open the Appstore page for TouchPlotLite

Follow this link to open the Appstore page for TouchPlot