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Hi,
I have a table of data as given below. I want a function or equation of the data. So that I can find the y value for desired x value.
Please guide me how to do that in Mathcad. I'm using Mathcad Prime 9.0
x | y |
6.2 | 215 |
9.1 | 153 |
13 | 111 |
15 | 97 |
18 | 82 |
22 | 67 |
24 | 62 |
27 | 55 |
30 | 50 |
33 | 46 |
36 | 42 |
39 | 39 |
43 | 35 |
47 | 33 |
51 | 30 |
Hi,
Thank you for the detail.
When I re-calculate Y using f(x) function, I'm getting values with +/-1.6 error. How to minimize the error further?
x | y (Existing data) | Y (Calculated data using function f(x)) | Error (y-Y) |
6.2 | 215 | 216.6173939 | -1.617393929 |
9.1 | 153 | 152.0112222 | 0.9887777664 |
13 | 111 | 109.3707378 | 1.629262187 |
15 | 97 | 95.83819461 | 1.161805388 |
18 | 82 | 80.99427715 | 1.005722847 |
22 | 67 | 67.29994691 | -0.2999469128 |
24 | 62 | 62.10633191 | -0.1063319106 |
27 | 55 | 55.70858169 | -0.7085816934 |
30 | 50 | 50.54613325 | -0.5461332521 |
33 | 46 | 46.28949998 | -0.2894999786 |
36 | 42 | 42.71728555 | -0.7172855481 |
39 | 39 | 39.6751177 | -0.6751176959 |
43 | 35 | 36.25596522 | -1.255965218 |
47 | 33 | 33.39831321 | -0.3983132065 |
51 | 30 | 30.97302218 | -0.9730221783 |
Change the assuming function Y(x):=ax^b such as ax^b+c, ax^3+bx^2+cx^1+d, etc..
Basically you have the choice between an interpolation or a function fit.
In case of an interpolation in Prime you have the choice between linear interpolation and cubic spline interpolation. An interpolated function runs exactly through all the given data points, but its behaviour inbetween might not always be as expected or desired.
In case of a function fit (regression) usually you get a function whose graph may not include any of the given data points exactly (as in Terrys appraoch) but gives an overall good fit. You have to guess which function type may apply as Prime provides not means to autoselect an appropriate function type like specialized programs like CurveExpert Pro will do.
If you need further help, come back here and ask and don't forget to attach your worksheet.
So first you will have to decide if you need an interpolation or a regression.
Here are a few examples for both: