Problem with implementation of the formula(e) - request for help
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Thread: Problem with implementation of the formula(e) - request for help

  1. #1
    Join Date
    Feb 2013
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    4

    Problem with implementation of the formula(e) - request for help

    Hello everyone. I am new on the forum, and also quite new to c++. Currently I develop some computational program, and have a problem with implementation of the formula(s). Let me explain this. I want to obtain smix:
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    wherein sk:
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    k = 0 - 4 (this is just naming for the 5 different substances, because the program computes some property of these substances, and the property of its mixture)
    x is a scalar, there are 5 such a scalars (for every k), so I put them into one vector
    dk, that is d0 - d4 are the 11 element coefficient vectors
    in the formula b is the 10 element vector, whose indexing begins from 1 (this is in the document from which the above formulas come), in the program indexing begins from 0, so bi element from the formula is b[i-1] in my program.
    I could simply implement this, no big deal - unless xk would not equal 0... When xk = 0, the natural logarithm cannot be computed, so i must add some checking if xk = 0, if yes the program should skip computing ln(xk) (sk should not be taken into account in that situation as well).
    I have tried to implement for/if combination, but it seems to surpass me... So I am kindly asking you - people of good will - to help me resolve the problem. I am stuck with this for a "while" and because of that kinda frustrated. I will be very, very very grateful for help. Thanks in advance.

  2. #2
    Join Date
    Dec 2012
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    Re: Problem with implementation of the formula(e) - request for help

    If you post the code you have for which you'd like some advice we'll offer our suggestions. If you do post, please format it before post and use code tags. Go Advanced, select code, click '#'

  3. #3
    Join Date
    Feb 2013
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    Re: Problem with implementation of the formula(e) - request for help

    Problem resolved.

  4. #4
    Join Date
    May 2009
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    Re: Problem with implementation of the formula(e) - request for help

    One possible simplification is that ln(T)^bi equals bi * ln(T). Then ln(T) becomes a constant of all summation terms and can be moved out and multiplied once only after summation.
    Last edited by nuzzle; February 17th, 2013 at 04:02 PM.

  5. #5
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    Feb 2013
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    Re: Problem with implementation of the formula(e) - request for help

    Firstly, ln(T)^bi does not equal bi * ln(T). Secondly, ln(T)^bi was not a problem. The problem was ln(xk), since xk can be 0. But thanks for willingness to help I finally figured out the solution.

  6. #6
    Join Date
    May 2009
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    2,413

    Re: Problem with implementation of the formula(e) - request for help

    Quote Originally Posted by Pederator View Post
    Firstly, ln(T)^bi does not equal bi * ln(T).
    No, it's ln(T^bi) that equals bi*ln(T). Sorry for that. Glad you caught it.

  7. #7
    Join Date
    Feb 2013
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    4

    Re: Problem with implementation of the formula(e) - request for help

    No problem pal.

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