Re: [boost] A question about Units & Spirit

Subject: Re: [boost] A question about Units & Spirit
From: John Phillips (phillips_at_[hidden])
Date: 2009-06-15 17:46:07

Daniel J. Duffy wrote:
> Thanks, John
> So I can just reply from here? Hope I'm doing it right this time :)
>  
> testing, testing..
> 
> Daniel
>  
> 

   Yes, you are in the right place. :-)

                        John

> ________________________________
> 
> From: boost-bounces_at_[hidden] on behalf of John Phillips
> Sent: Mon 08-06-2009 21:59
> To: boost_at_[hidden]
> Subject: [boost] A question about Units & Spirit
> 
> 
> 
>    In the middle of the directX thread, Daniel Duffy asked a question
> that seems more suited to its own thread. I'm starting that thread and
> giving others a chance to join into the discussion by giving you the
> content of the few messages that have passed by so far.
> 
>                         John
> 
> 
>  From Daniel ---------------------------------------------------
> 
> Hello,
> This is my first mail, so I hope I have sent it to the right address  :)
> 
> I am using the Units library for Dimensional Analysis. So far it is very
> useful. Up till now I am using it in a hard-coded/compile time way as in
> a test.cpp.
> 
> My inteterst is in using Units as part of a larger run-time system so I
> need some way of making my code more flexible. Lambda library is an
> option here but I would also like to create units and quanties from
> string input as well as being able to parse these strings to units and
> then store the units in a database.
> 
> Can I use Spirit (and Serialization) for these features? Maybe the
> functionality already exist, and I have not found it.
> 
> best regrads
> 
> Daniel J. Duffy
> 
> 
> 
>  From Hartmut ---------------------------------------------------
> 
> Sure Spirit is your friend for all parsing and output generation needs.
> What did you have in mind?
> 
> Regards Hartmut
> 
> 
> 
>  From Daniel ----------------------------------------------------
> 
> Hartmut,
> I would like to generate well-formed units and create expressions of the
> followiong kinds:
> 
> Examples of unit expressions:
> 1.       2m + 15m*32s/16s = 32m.
> 2.       3m*7s + 2m*10s/5m = 21m + 4s -> ERROR. Can't add meters to
> seconds.
> 
> The second group looks more tricky.
> 
> Examples of simplification:
> 1.       (x-2)2 + 4x2 - 2^x + 1 = 5x2 - 8x + 10
> 2.       x2 + 7x + 10 = (x + 2)(x + 5)
> 3.       (a + b)(a - b) = a2 - b2
> 4.       sin(x)2 + cos(x)2 = 1
> 5.       2sin(x)cos(x) = sin(2x)
> 
> One tricky part is for example #5 where the code needs to 'know'
> trigonometry.
> 
> best regards
> 
> Daniel
> 
> 
> 
>  From John ----------------------------------------------------------
> 
> Daniel J. Duffy wrote:
>  > Hartmut,
>  > I would like to generate well-formed units and create expressions of
> the followiong kinds:
>  >
>  > Examples of unit expressions: 1.       2m + 15m*32s/16s = 32m. 2.
>     3m*7s + 2m*10s/5m = 21m + 4s -> ERROR. Can't add meters to seconds.
> 
>    So, you want this to happen at run time, or at compile time? At
> compile time, I think you are already set with the Units library. At run
> time, there are examples with the library that would help.
> 
>    If parsing the input is your concern, then Spirit is a good choice.
> (Spirit 2 is even better, by the way.)
> 
>    Using the two together, you could write a program where a user enters
> your example lines and gets correct responses.
> 
>  >
>  > The second group looks more tricky.
>  >
>  > Examples of simplification: 1.       (x-2)2 + 4x2 - 2^x + 1 = 5x2 -
> 8x + 10 2.       x2 + 7x + 10 = (x + 2)(x + 5) 3.       (a + b)(a - b) =
> a2 - b2 4.       sin(x)2 + cos(x)2 = 1 5.       2sin(x)cos(x) = sin(2x)
>  > One tricky part is for example #5 where the code needs to 'know'
> trigonometry.
> 
>    As far as I can tell here, you are looking for a program that does
> symbolic algebra. If that is true, then I don't think boost has a
> complete solution for you.
> 
>    Writing the parser for the input with Spirit wouldn't be that bad,
> but writing the processing engine that matches patterns and does
> simplifications is not covered by any current Boost libraries. I don't
> recall seeing anyone poll for interest on this, so I don't think there
> is even a partial library in the sandbox.
> 
>    Would you want this at run time, compile time, both? I haven't tried
> to write it, but I think a pure compile time implementation would be
> prohibitively slow. For a pure run time solution, you might consider
> linking to already existing solutions, such as Maple or Mathematica.
> 
>  >
>  > best regards
>  >
>  > Daniel
>  >
> 
> 
>              John
> 
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