Form an equation from table data

[MP_10748008]

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

[ttokoro]

Check Prime help of minner. It shows how to do it.

[MP_10748008]

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

[ttokoro]

Change the assuming function Y(x):=ax^b such as ax^b+c, ax^3+bx^2+cx^1+d, etc.. 

[achirila]

Hi @MP_10748008 

It looks like you have some responses from some community members. If any of these replies helped you solve your question please mark the appropriate reply as the Accepted Solution. 

Of course, if you have more to share on your issue, please let the Community know so other community members can continue to help you.

[Werner_E]

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: