March 2009 - Boost - lists.preview.boost.org

Re: [boost] [math] Does any one interesting in calculating derivative for a expression automatically?
by Dongfei Yin 04 Mar '09

04 Mar '09

Hi John, 1. I have tried that if you write d(d(d(d(x*x*x*x, x), x), x), x), it will take a long compile time without optimized. I have do something to optimized it. I need to write a lot of specialized template class for most of the operators. 2. Because of the C++ grammar, I think it can just accept expression like C++ style. think about operator^, the priority is lower in C++ than in math. 3. As I said, high derivative will cost lots of compile time without "simplify", so you are right, the expression should be simplified. but at compile time, it is a little difficult to do it, but I'll do my best to optimized it. Dongfei. > Good idea, and this is all very neat, but I see a couple of issues: > > 1) Compile times for a compile time derivative is likely to be slow? > 2) Isn't it easier to just calculate the derivative within a symbolic math > package and then cut and paste the result into your code (Yacas is free for > example)? > 3) What happens for very complex expressions? Can the compile time code > simplify the resulting derivative so that it is optimally evaluated? Most > symbolic math packages will have a "simplify" function that does just that, > without it, code might be very inefficient to evaluate, with it, compile > times might be way too long :-( > > Regards, John. >

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Re: [boost] [math] Does any one interesting in calculating derivative for a expression automatically?
by Dongfei Yin 04 Mar '09

04 Mar '09

Hi Mukkul, I have implement the trigonometric terms. only sin and cos. it can add new operator into it easily. this expression d(cos(_x * _x) , _x) will return a functor, at last, the computation is done by std::sin : ) Dongfei. > HI Dongfei, > > I am interested in it. But what the plan is exactly ? How you are going to do it > for say expressions involving trigonometric terms ? For polynomial expressions > things are manageable, how you are going to parse other complex expressions ? > > BTW how you are going to take care of algebra at many places ? > > With Regards, > Reetesh Mukul >

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Re: [boost] [math] Does any one interesting in calculating derivative for a expression automatically?
by Dongfei Yin 04 Mar '09

04 Mar '09

Hi Kasra, I am very glad that you are interesting in it. Now, it can just calculate polynomial, and sin, cos. what should I do to upload the source? I am not so familiar with this system. Dongfei. > I think the function are rather interesting in fact I really like differential calculations with the way you have implemented it. > > If you give more information about your implementation maybe we could work something out. > > > -- Kasra >

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[math] Does any one interesting in calculating derivative for a expression automatically?
by Dongfei Yin 04 Mar '09

04 Mar '09

Hi, Recently, I am working on some mathematical issues, most of my working time, I am calculating the derivative of function manually, it is such a tedious work that I write a piece of code to do it for me. now I want to share it with others. Let me show it for you. it it something like lambda expression, I mean boost::lambda. but the main purpose is to calculate derivative. As lambda do, I defined some variables like _x, _y in advance. A function named "d" can calculate derivative. then we can use it like this. d(_x * _x , _x)(1.0); // f(x)=x*x, f '(x) = 2x. so the result will be f '(1.0) = 2.0. d(d(_x * _x, _x), _x)(4.0); // f(x)=x*x, f ''(x) = 2, so the result will be f ''(4.0) = 2.0; this argument is just used to determine the return type. of cause it can work with more than one variables, such as, d(_x * _y, _x)(2.0, 1.0); // f(x,y)=x*y, f 'x(x,y)=y, so the result will be f 'x(x,y)=1.0; // the first argument will be ignored. d(d(_x * _y, _x), _y)(1.0); // f(x,y)=x*y, f ''xy(x,y)=0, so here one or two argument are all OK. and it can calculate derivative for some complicated expressions. theoretically, it can calculate high derivative for a expression as high as you want until the expression become zero. I want to share it with others, but it is not so perfect now. I need some suggestion to make it better. by the way, I am a new face, and English is not my native language, so if I did not explain some thing clearly, please do ask me. I will do my best to clarify.

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[convert] Default Syntax Idea
by Stewart, Robert 04 Mar '09

04 Mar '09

I was thinking a bit about syntax for the default value for the notional boost::convert() and kin. How about the following: int const i(3); string const s("something"); int const j(convert<int>(s) | 5); convert<DestType,SourceType>(SourceType) can return a type which throws on failure in operator DestType(), but has an operator |(SourceType) which returns a second type constructed with the SourceType value. The second type provides its own operator |(SourceType) which returns that value in its operator DestType() on failure. Returning a default value in lieu of an exception is a special case; it ought not be treated like formatting. Thus, while Boost.Parameter might be appropriate to package the extra information desired for formatting, I don't like the idea of writing "default_ = 5" in the call, and I don't think ", 5" in the argument list is as clear as it could be. The syntax above is obvious and concise while being distinct from whatever may be done for formatting. _____ Rob Stewart robert.stewart(a)sig.com Software Engineer, Core Software using std::disclaimer; Susquehanna International Group, LLP http://www.sig.com IMPORTANT: The information contained in this email and/or its attachments is confidential. If you are not the intended recipient, please notify the sender immediately by reply and immediately delete this message and all its attachments. Any review, use, reproduction, disclosure or dissemination of this message or any attachment by an unintended recipient is strictly prohibited. Neither this message nor any attachment is intended as or should be construed as an offer, solicitation or recommendation to buy or sell any security or other financial instrument. Neither the sender, his or her employer nor any of their respective affiliates makes any warranties as to the completeness or accuracy of any of the information contained herein or that this message or any of its attachments is free of viruses.

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[thread] thread-safe static local
by Oliver Kowalke 04 Mar '09

04 Mar '09

Hi, I need a function 'get_default_X()' returning a reference to a singleton in a multithreaded env. I choosed Scott Meyers singleton pattern (static local) together with boost::call_once(). My this be a reasonable, threadsafe implementation? regards, Oliver -- Computer Bild Tarifsieger! GMX FreeDSL - Telefonanschluss + DSL für nur 17,95 ¿/mtl.!* http://dsl.gmx.de/?ac=OM.AD.PD003K11308T4569a

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Boost.Test: documenting a little Mac OS X usage nit
by Owen Smith 03 Mar '09

03 Mar '09

Greetings! I'd like to present a little tiny puzzle that took me an embarrassingly long time to solve--a year, to be specific. (OK, maybe a day poking around, followed by a year being buried in the bug queue. :-) ) With this comes a couple of requests for the Boost.Test documentation. If i understand correctly, the Boost.Test library boost_unit_test_framework is a little bit odd in that the static version of the library carries a main() routine (which I intend to take advantage of) whereas the dynamically linked version does not. In Mac OS X, with the standard MacPorts installation of boost, this poses a problem because both static and dynamic libraries are built and installed to the same location. When linking with gcc using my usual -L and -l options, given the choice, the linker will always select the dynamic library, and I will be missing my main(). (I should point out this would be a non-issue if the main() routine were in a different library that you could choose to include or not include as you wish, but I'm assuming this battle has long since been fought and resolved.) First, I know the main() issue has been mentioned many times on the list before, but I couldn't find any documentation of it in the 1.38.0 manual. This seems like a significant issue to document--am I just missing it somewhere? Second, the best workaround we found for this problem was to explicitly select the static library by foregoing the -L and -l options and directly specifying <full-path>/libboost_unit_test_framework-mt.a as one of the linker arguments. And this is what I'd like to see documented--either as a footnote to "Unit Test Framework > User's guide > Usage variants > Static library", or maybe as part of the topic "Unit Test Framework > Usage recommendations > Generic". I'm happy to prepare documentation patches if desired. Thanks! -- O

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[math] Does any one interesting in calculating derivative for a expression automatically?
by Kasra 03 Mar '09

03 Mar '09

Hi, I think the function are rather interesting in fact I really like differential calculations with the way you have implemented it. If you give more information about your implementation maybe we could work something out. -- Kasra

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boost::bind, problem with result type deduction and calling conventions
by Ingo.Loehken＠boc-eu.com 03 Mar '09

03 Mar '09

hi, anybody able to explain, why the code for the result type, related to special calling conventions defines an void return type ? template< class R, class T > struct add_cref< R (T::*) (), 1 > { typedef void type; }; so that code like class A { public: int __stdcall x() { return 0; } void const y() {} explicit A() { typedef boost::function<int()> fun_t; fun_t const f(boost::bind(&A::x,this)); } }; ends up with an warning at bind 1>G:\boost\boost_1_37_0\boost/bind.hpp(1643) : warning C4180: qualifier applied to function type has no meaning; ignored 1> G:\boost\boost_1_37_0\boost/bind.hpp(1682) : see reference to class template instantiation 'boost::_bi::add_cref<Pm,I>' being compiled 1> with 1> [ 1> Pm=int (__stdcall Ado::A::* )(void), 1> I=1 1> ] 1> G:\dev\workspace\files\ado\ado_bind.hxx(36) : see reference to class template instantiation 'boost::_bi::dm_result<Pm,A1>' being compiled 1> with 1> [ 1> Pm=int (__stdcall Ado::A::* )(void), 1> A1=Ado::A * 1> ] because the proposed specialization is not choosen by the compiler. Adding an __stdcall to the function signature type in add_cref fixes that problem, but still i do no understand, why the defintion is not like template< class M, class T > struct add_cref< M (__stdcall T::*) (), 1 > { typedef M const& type; }; and of course that fix is only applicable for __stdcall, where specialzations for other calling conventions can easily be generated, like for mem_fn_cc in respect to requested support for calling conventions. Thanks for your help, ILo. compiler : msvc 8.0 library : boost 1.38

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Headers erased after the first building in VC8 of boost 1.38
by Trimoldi, F. (Filippo) 03 Mar '09

03 Mar '09

I generated a Boost.sln solution for VC8 with the new system CMake. ( using this command: cmake -DCMAKE_IS_EXPERIMENTAL=YES_I_KNOW CMakeLists.txt in root directory of the boost ) When I try to build the entire solution all thinks goes good without problem. But only the first time. In fact, at the end of this first building all the headers are erased from the boost the directory. So I cannot make another building and I have to recover the headers file by other ways. Have you got the same problem? This e-mail and its contents are subject to the DISCLAIMER at http://www.tno.nl/disclaimer/email.html

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