Re: Re: The audience for Mathematica

*To*: mathgroup at smc.vnet.net*Subject*: [mg102179] Re: [mg102150] Re: The audience for Mathematica*From*: "David Park" <djmpark at comcast.net>*Date*: Fri, 31 Jul 2009 05:58:15 -0400 (EDT)*References*: <31768270.1248950619222.JavaMail.root@n11>

Alexei, Easy with Presentations. These are just cases where you want to apply Factor to selected portions of a sum. The MapLevelParts command allows you to do that (as opposed to ReplacePart that acts independently on each part.) Needs["Presentations`Master`"] expr = -a^2 b^2 c^2 + 4 a^3 c^3 + 4 a^2 b^3 d - 18 a^3 b c d + 27 a^4 d^2 To obtain the first form: expr // MapLevelParts[Factor, {{2, 4}}] % // MapLevelParts[Factor, {{1, 2, 3}}] % // MapLevelParts[Factor, {2, 2, {1, 2}}] giving -a^2 b^2 c^2 + 4 a^2 b^3 d + 27 a^4 d^2 + 2 a^3 c (2 c^2 - 9 b d) 2 a^3 c (2 c^2 - 9 b d) + a^2 (-b^2 c^2 + 4 b^3 d + 27 a^2 d^2) 2 a^3 c (2 c^2 - 9 b d) + a^2 (27 a^2 d^2 + b^2 (-c^2 + 4 b d)) The last command, for example, says to use Factor on parts 1 and 2 of the second part of the second part of the previous expression. To obtain your second form of the expression use: expr // MapLevelParts[Factor, {{2, 5}}] % // MapLevelParts[Factor, {{2, 3}}] Giving -a^2 b^2 c^2 + 4 a^2 b^3 d - 18 a^3 b c d + a^3 (4 c^3 + 27 a d^2) -a^2 b^2 c^2 - 2 a^2 b (-2 b^2 + 9 a c) d + a^3 (4 c^3 + 27 a d^2) This is all what I call 'doing surgery on expressions' and doing it with Mathematica is less error prone than doing it by hand. The Manipulations section of Presentations has a number of convenient routines for doing surgery: CompleteTheSquare, FactorOut, AddZero, MultiplyByOne, LinearBreakout, PushOnto, HoldOp, CreateSubexpression, MapLevelParts, MapLevelPatterns, EvaluateAt, EvaluateAtPattern, LHSSymbolsToPatterns. David Park djmpark at comcast.net http://home.comcast.net/~djmpark/ From: Alexei Boulbitch [mailto:Alexei.Boulbitch at iee.lu] Dear Community, This question seems to be an important one, if to judge by the number of comments. I would like to look at this problem from a little bit different perspective. I belong to the group #3 according to AES classification cited below. And as such, I see great advantages of Mathematica for me and for people like myself, as well as lacks of some properties that Mathematica might, but does not have. Therefore, it may be a constructive idea to make a list of such desired features classified according to classes of Mathematica users like the ones cited below. This may help the developers in their great and difficult work. Here I start from myself and invite you to do the same, if you would like to. What I badly need are instruments that would enable one to easily bring an expression to a desired form when making analytical transformations. Let me explain this in more details. Operations like Simplify, Apart, Factor etc. make a great job. However, when the answer is lengthily it often helps, if one can group terms in the answer, factorize some parts of those terms separately from one another. Here it is important that transformation should go not automatically (like it goes now when say, Simplify is applied). What I have in mind is a complete control of the transformation applied on different levels of the expression by the user together with a possibility to apply simultaneously different operations on different levels and to different parts of the same level. To give an example, (just the first that that I could think of) here is a simple algebraic expression which is grouped and factorized in different ways: expr = -a^2 b^2 c^2 + 4 a^3 c^3 + 4 a^2 b^3 d - 18 a^3 b c d + 27 a^4 d^2 = =a^2 (b^2 (-c^2 + 4 b d) + 27 a^2 d^2) + 2 a^3 c (2 c^2 - 9 b d) = =a^3 (4 c^3 + 27 a d^2) - 2 a^2 b (-2 b^2 + 9 a c) d - a^2 b^2 c^2 Such transformations may result in a further simplification that is not most simple according to the Mathematica criterion, but is most simple from the user point of view. It may also help in understanding of relative contributions of terms and may enable one to neglect some and thus, to further simplify the whole expression and so on. That is how we worked during the pre-Mathematica era, and it often brought a success. I know people (and many of them) who made important contributions just because they zealously rewrote and rewrote long expressions many times in many different forms until they have found advantageous ones. At present sometimes it is also possible to do so on-screen (e.g. without going to the paper as an intermediate step), but (i) not in all cases, (ii) this requires programming which is not always evident and (iii) because of this it draws one away from his primary subject to a secondary one (e.g. to programming). Please understand me correctly: what already exists is already great. I do not propose to refuse of it (or of any its part). What I would like to, is to have an additional tool, to be applied when necessary by those who need it. Therefore, it would be great, if in say, next Mathematica version some tools would be introduced helping to fulfill such tasks. Let me also comment few words on the discussion nucleated by the contribution of Helen Reed, to its part concerning advantages and dangers of Mathematica in teaching. As much as I understand it, it is a methodological, rather than "ideological" problem. That is, application of Mathematica for teaching requires a special approach. One has to think carefully of what could and should be done and how, and what should not be done. Applying Mathematica for teaching without thinking may of coarse, make harm. But who says that we should apply it without thinking? Development of the methodology of class-room application of Mathematica is non-trivial. For this reason it is important to share such a methodological experience among those who do such work. I wish you all a success, Alexei // /From/: AES As a more specific definition of an expected audience, it seems to me (and, I think, Helen Read) that Mathematica -- or at least a more consistent and less perplexing form of Mathematica: 1) Could be very accessible to bright high school students, maybe with some hand holding; 2) Could be (and to some extent is) useful to average college students and to working BS level engineers as a helpful working tool in any technical or mathematically oriented area; and 3) Could be (and to a considerable extent is) a very, very powerful personal hands-on tool for graduate students, faculty, designers, engineers, and researchers for doing real work in a very wide range of fields (not just engineering, math or science). And that's a very massive audience. (Note that I'm writing here about people whose primary focus is on, and whose energies are primarily devoted to, the work they want to do -- the problems they want to solve -- and who do not want to convert their primary focus to becoming a Mathematica expert.) Of course, there's the alternative audience of professional Mathematica experts, whose full time or near full time occupation is becoming expert at using Mathematica, with all its complexities and perplexing features. That's a much smaller audience. (And to be just a little snide here, many of those people are essentially "programmers", who are hired as such by the upper levels of my audience #3 above.) -- Alexei Boulbitch, Dr., habil. Senior Scientist IEE S.A. ZAE Weiergewan 11, rue Edmond Reuter L-5326 Contern Luxembourg Phone: +352 2454 2566 Fax: +352 2454 3566 Website: www.iee.lu This e-mail may contain trade secrets or privileged, undisclosed or otherwise confidential information. If you are not the intended recipient and have received this e-mail in error, you are hereby notified that any review, copying or distribution of it is strictly prohibited. Please inform us immediately and destroy the original transmittal from your system. Thank you for your co-operation.

**Re: The audience for Mathematica (Was: Re: Show doesn't work inside**

**Re: The audience for Mathematica**

**Skellam distribution**