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Math Help - findfit mathematica

  1. #1
    Newbie
    Joined
    Dec 2009
    Posts
    1

    findfit mathematica

    Hello


    I have a list whit numbers in the form {{x1,y1},{x2,y2}...} if i plot the numbers i get a plot that almost looks like E^x (E= 2,71).

    I want to create a function that follows my numbers i have tried to use FindFit[data,a*E^x,a,x] in mathematica to do that but i am failing. The function i get dosent reflect the numbers i have.

    I would be very happy if anyone could help me whit the Findfit function.
    I belive that the problem is caused by the expression that is probably wrong (a*E^x) but i dont know how to write a working expression that fit my values.

    This is the numbers i use:

    {30, 0.095}, {31, 0.125}, {32, 0.094}, {33, 0.109}, {34, 0.109}, {35, \
    0.125}, {36, 0.151}, {37, 0.156}, {38, 0.172}, {39, 0.282}, {40, \
    0.265}, {41, 0.328}, {42, 0.36}, {43, 0.531}, {44, 0.594}, {45, \
    0.812}, {46, 0.995}, {47, 1.531}, {48, 10.016}, {49, 10.093}, {50, \
    15.644}, {51, 17.025}, {52, 21.}, {53, 26.844}, {54, 28.078}, {55, \
    35.976}, {56, 47.985}, {57, 60.406}, {58, 84.533}, {59, 118.786}, \
    {60, 170.345}, {61, 308.687}, {62, 426.375}, {63, 658.689}, {64, \
    937.593}, {65, 1230.61}, {66, 1729.16}, {67, 2143.65}, {68, 2698.39}, \
    {69, 3497.201}, {70, 4117.}, {71, 6447.02}, {72, 9233.23}, {73, \
    10821.2}
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  2. #2
    Super Member
    Joined
    Jan 2009
    Posts
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    Quote Originally Posted by user1234 View Post
    Hello


    I have a list whit numbers in the form {{x1,y1},{x2,y2}...} if i plot the numbers i get a plot that almost looks like E^x (E= 2,71).

    I want to create a function that follows my numbers i have tried to use FindFit[data,a*E^x,a,x] in mathematica to do that but i am failing. The function i get dosent reflect the numbers i have.

    I would be very happy if anyone could help me whit the Findfit function.
    I belive that the problem is caused by the expression that is probably wrong (a*E^x) but i dont know how to write a working expression that fit my values.

    This is the numbers i use:

    {30, 0.095}, {31, 0.125}, {32, 0.094}, {33, 0.109}, {34, 0.109}, {35, \
    0.125}, {36, 0.151}, {37, 0.156}, {38, 0.172}, {39, 0.282}, {40, \
    0.265}, {41, 0.328}, {42, 0.36}, {43, 0.531}, {44, 0.594}, {45, \
    0.812}, {46, 0.995}, {47, 1.531}, {48, 10.016}, {49, 10.093}, {50, \
    15.644}, {51, 17.025}, {52, 21.}, {53, 26.844}, {54, 28.078}, {55, \
    35.976}, {56, 47.985}, {57, 60.406}, {58, 84.533}, {59, 118.786}, \
    {60, 170.345}, {61, 308.687}, {62, 426.375}, {63, 658.689}, {64, \
    937.593}, {65, 1230.61}, {66, 1729.16}, {67, 2143.65}, {68, 2698.39}, \
    {69, 3497.201}, {70, 4117.}, {71, 6447.02}, {72, 9233.23}, {73, \
    10821.2}
    The attached image is a plot of the x values against the log of the ordinates. It appears as if you may have polynomial of degree 20.

    I tried several methods to smooth the data and get a reasonal fit.
    The abrupt step (at points 47/48) is the problem.
    Is this one set of data or a merged file?
    Attached Thumbnails Attached Thumbnails findfit mathematica-plot1.jpg  
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