From: Andrew Miller <ak.miller@auckland.ac.nz>

Date: Mon, 20 Nov 2006 17:02:39 +1300

Message-ID: <456128DF.9050702@auckland.ac.nz>

To: "For those interested in contributing to the development of CellML." <cellml-discussion@cellml.org>, www-math@w3.org

Date: Mon, 20 Nov 2006 17:02:39 +1300

Message-ID: <456128DF.9050702@auckland.ac.nz>

To: "For those interested in contributing to the development of CellML." <cellml-discussion@cellml.org>, www-math@w3.org

Peter Jipsen wrote: > Hi Andrew, > > For an interesting comparison you could look at ASCIIMathML > http://www1.chapman.edu/~jipsen/mathml/asciimath.html and the syntax > that was chosen for the plain text to Presentation MathML translation. > Since this is done on the fly in JavaScript, it had to be very simple > and fast, so there are some compromises in the quality of the PMathML > that is generated, but the input syntax is very natural (even for > undergraduate students). As would be expected for presentation MathML input language, it seems much of your language is orientated towards specifying layout. However, there are a few features in your language which would probably be useful in a content MathML input language: 1) I note you use ^ for superscripts. This could be used in content MathML input languages for exponentiation (the only problem with this, of course, is that ^ is used in-order in many programming languages to mean exclusive-or, as well as exponentiation in others). 2) I note that you treat certain strings, like sqrt, as being functions, even without intervening whitespace, e.g. to allow sqrtx. I'm not sure I like this, because it makes a large block of variables names ambiguous with a function, which would require some sort of escape syntax. > > My experience with ease-of-use for typing math is to make the ascii > look as much as possible like the math that it represents. This is > what users would guess without reading a manual (and who does that > nowadays?:-). I agree to some extent (hence why I am proposing in-order operators where the mathematics used in written publications commonly uses them, and pre-order operators everywhere else). For more complex constructs like derivatives, which have several common forms, I'm not sure how easy it is for users to guess straight off anyway. I think simplicity (so that if they do look up the rules, they will remember them for next time, and so they can quickly learn from examples), and similarity to existing languages (where possible) are probably more important goals here. > > For Content MathML you are asking some important questions. I believe > the bracketing structure should be preserved, so a+b+c should not be > nested, but a+(b+c) should be nested in the CMathML. Not all > interpretations of + necessarily insist that these two formulas > evaluate to the same value (in fact in most programming languages with > a maxint limit they can differ because of overflow). The way you have bracketed your example changed the precedence, so strays slightly from my original question (after all, if you substituted + for - in your example, you would change the result even for real-valued variables). Comparing a+b+c with (a+b)+c is more interesting, because the order of operations in the same. This is actually a slight discrepancy between content MathML (where plus is an n-ary operator) and and the standard approach for studying groups in mathematics (because the usual definition of a group makes the operator a binary operator). I am not aware of any document which defines how the n-ary operators on a variable in content MathML map onto the binary operator plus. However, my interpretation is that if Xi are members of a group on addition (for all i), then plus(X1,X2,...,Xn) = plus(X1,X2,...,Xn-1) + Xn (n > 2) plus(X1,X2) = X1 + X2 In this case, the value of the expression is not changed between a+b+c and (a+b)+c, and therefore, the meaning shouldn't be changed (the only case to worry about is that the semantics of n-ary plus could be changed by definitionURL, in which case the assumption that the two MathML trees are equivalent would not hold. However, CellML is intended for the interchange of mathematical models, so using definitionURL would harm this goal and be bad anyway, and secondly, it is unclear whether the a+b+c case should use the tertiary form, or if it should be folded by the precedence rules into two binary operations). > > For differentiation, how about d/(dx)(f(x)) or d/dx(f(x)) and > del/delx(f(x)) for partial derivatives? There are some minor issues here, especially if there are variables called d and dx in the CellML component. Then, there could be ambiguity between <apply><divide/> <ci>d</ci> <ci>dx</ci> </apply> Pushing the d together with the bound variable name could potentially be confusing (variable names in CellML are frequently more than one character long, so I would find it easier to understand an equation if there was a bracket after the d). The other issue (this might be a somewhat CellML specific issue, and not generalise to other users of content MathML) is that most CellML models that use the diff operator do so to define systems of ordinary differential equations, and so they will almost always take the derivative of one variable with respect to another. It is rare to see papers on these types of models use the differention operator, so the d(x)/d(time) notation makes more sense than d/d(time)(x) (unless we are going to have both forms). Best regards, AndrewReceived on Monday, 20 November 2006 04:02:54 UTC

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