I have a plotted spectral curve in google sheets. All points are real coordinates. As you can see, data is not provided for the slope below 614nm. I would like to extend the slope beyond the supplied data, so that it reaches 0. In a mathematically relevant way to follow the trajectory it was taking from when the slope started. Someone mentioned to me I would have to potentially use a linear regression? I'm not sure what that is. How would I go about extending this slope relevant to it's defined trajectory down to 0 in google sheets?

Here's the data

x-axis:

614
616
618
620
622
624
626
628
630
632
634
636
638
640
642
644
646
648
650
652
654
656
658
660
662
664
666
668
670
672
674
676
678
680
682
684
686
688
690
692
694
696
698
700
702
704
706
708
710
712
714
716
718
720
722
724
726
728
730

y-axis:

0.7101
0.7863
0.8623
0.9345
1.0029
1.069
1.1317
1.1898
1.2424
1.289
1.3303
1.3667
1.3985
1.4261
1.4499
1.47
1.4867
1.5005
1.5118
1.5206
1.5273
1.532
1.5348
1.5359
1.5355
1.5336
1.5305
1.5263
1.5212
1.5151
1.5079
1.4994
1.4892
1.4771
1.4631
1.448
1.4332
1.4197
1.4088
1.4015
1.3965
1.3926
1.388
1.3813
1.3714
1.359
1.345
1.3305
1.3163
1.303
1.2904
1.2781
1.2656
1.2526
1.2387
1.2242
1.2091
1.1937
1.1782

Thanks

CodePudding user response：

I understand that you want The curve should be increased beyond the given data in a mathematically sound fashion until it approaches 0, In what follows, I'm going to show how it's done with the last 2 data points which make the filled data linear it might help, like this: take a look at

We need to

1 - Paste this SEQUENCE function formula in C3 to get the order of input

=SEQUENCE(COUNTA(B3:B),1,1,1)

2 - SORT the the input by pasting this formula in E3.

=SORT(A3:C61,3,0)

3 - In F62 after the last line of the sorted data paste this TREND function that Fits an ideal linear trend using the least squares approach to incomplete data about a linear trend and/or makes additional value predictions..

=TREND(F60:F61,E60:E61,E62:E101)

TREND takes
'known_data_y' set to F60:F61
'[known_data_x]' set to E61,E62 those are the 2 data point
[known_data_x] set to E62:E101, we get it by pasting E62:E101 after the last line of the sorted data in "x-axis:" in output table cell E62

4 - To see the newly genrated data in the red curve we need a new column that start from K62 till the very bottom of the data "y-axis:" in output table cell K62, by pasting this ArrayFormula in K62.

=ArrayFormula(E62:G101)

5 - Add a Serie in tne chart in chart editor > setup > Series > Add Serie.