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Thread: Help with formula for curve

  1. #1

    Help with formula for curve



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    Have been looking for a formula to give me a curve similar to the following:-

    will post this 5 times untill I can post a link

    Solid blue line. Doesn't matter if it doesn't exactly fit, I think I can adjust the functions by trial and error once I get it into xls. I am after the y value by inputting the x value, the important bit being the the curve rises steeply, tails off but never starts to go back down as would a quadratic equation ( y=ax2+bx+c ) If someone has something it would be great, have been looking for what seems like ages, many thanks in advance
    Paul M
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  2. #2
    It's an inverse exponential curve, not a quadratic.

    Something of the formula y = 1- exp(-x)



    Quote Originally Posted by Paul M View Post
    Have been looking for a formula to give me a curve similar to the following:-

    will post this 5 times untill I can post a link

    Solid blue line. Doesn't matter if it doesn't exactly fit, I think I can adjust the functions by trial and error once I get it into xls. I am after the y value by inputting the x value, the important bit being the the curve rises steeply, tails off but never starts to go back down as would a quadratic equation ( y=ax2+bx+c ) If someone has something it would be great, have been looking for what seems like ages, many thanks in advance
    Paul M

  3. #3
    Quote Originally Posted by evohnave View Post
    It's an inverse exponential curve, not a quadratic.

    Something of the formula y = 1- exp(-x)
    Thanks but that just seems to give the answer of 1 whatever the value of X is used, forgive me if I'm doing something wrong, I am a real beginner.

  4. #4
    Easiest approach:

    Column A: Put "X" in A1. Put a 0 in A2, select "Fill" in the editing section of the Home tab, select series, Series in Columns, Type Linear (default), Step Value 0.1, Stop Value 5. This will give you your x data
    Column B: Put "Y" in B1. Put the following formula in B2: =1-EXP(-A1)
    Copy B2 down through B52

    Now you have your data.

    Select the data B1:B52

    Insert a line chart.

    Right click on the chart, "Select Data"

    Under Horizontal (Category) Axis Labels click edit

    In the Axis Label Range, click on the little chart symbol to the right, then click on A2, hold the shift key, and press ctrl and the down arrow at the same time. The box should now read =Sheet1$A$2:$A$52 or similar (depending on your sheet's name). Press enter. Press OK. Press OK.

    Play with your chart and label it, change the line color, etc etc.

  5. #5

  6. #6
    Quote Originally Posted by evohnave View Post
    Easiest approach:

    Column A: Put "X" in A1. Put a 0 in A2, select "Fill" in the editing section of the Home tab, select series, Series in Columns, Type Linear (default), Step Value 0.1, Stop Value 5. This will give you your x data
    Column B: Put "Y" in B1. Put the following formula in B2: =1-EXP(-A1)
    Copy B2 down through B52

    Now you have your data.

    Select the data B1:B52

    Insert a line chart.

    Right click on the chart, "Select Data"

    Under Horizontal (Category) Axis Labels click edit

    In the Axis Label Range, click on the little chart symbol to the right, then click on A2, hold the shift key, and press ctrl and the down arrow at the same time. The box should now read =Sheet1$A$2:$A$52 or similar (depending on your sheet's name). Press enter. Press OK. Press OK.

    Play with your chart and label it, change the line color, etc etc.
    Aha , many thanks, I was putting in large numbers for X not 0.1, 0.12 etc, need big numbers but can multiply them down and up of course. Many thanks

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