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Math Help - Number relations

  1. #1
    Newbie
    Joined
    Oct 2008
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    1

    Cool Number relations

    Hi All,

    I have a small maths problem. I am trying to create a relationship between two sets of numbers. The non-linear value comes from a light sensor and the other set of values are LUX levels. The values are as follows :-

    LUX Value
    10, 40800
    20, 26500
    30, 20400
    40, 17000
    50, 14700
    60, 13020
    70, 11780
    80, 10750
    90, 10230
    100, 9320

    I have plotted these values out and they appear to give a decaying exponential curve. What I am aiming for is two cells in excel, one in which I can enter a LuX value and the other cell will display the associated ohms value.

    Regards,

    Andrew.
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  2. #2
    MHF Contributor

    Joined
    Apr 2005
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    Quote Originally Posted by Meppso View Post
    Hi All,

    I have a small maths problem. I am trying to create a relationship between two sets of numbers. The non-linear value comes from a light sensor and the other set of values are LUX levels. The values are as follows :-

    LUX Value
    10, 40800
    20, 26500
    30, 20400
    40, 17000
    50, 14700
    60, 13020
    70, 11780
    80, 10750
    90, 10230
    100, 9320

    I have plotted these values out and they appear to give a decaying exponential curve. What I am aiming for is two cells in excel, one in which I can enter a LuX value and the other cell will display the associated ohms value.

    Regards,

    Andrew.
    If (x,y) appears to have a decaying exponential curve, that is if y= Ae^{kx}, then log y= log A+ kx, a linear relation. You can convert your list to (x, log y) and find a least squares line Y= kx+ b where Y= log y. Then  A= e^b
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