first derivative

michaelg2708

New Member
Joined
Apr 11, 2018
Messages
9
how do i get the first derivative of this data? i would like something that ends up like the orange line on the bottom graph if thats possible. i am trying to find the turning points on the graph and i think the first derivative is the best way to go? thanks
1640197506613.png

graph.xlsx
AB
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Sheet1
 

Excel Facts

What did Pito Salas invent?
Pito Salas, working for Lotus, popularized what would become to be pivot tables. It was released as Lotus Improv in 1989.
Taking the difference between successive points (column B) gives you the discrete derivative. Anywhere that derivative crosses zero is an inflection point. But your data seems to be all over the place and there are inflection points everywhere.

I filtered out the constant data and found 282 inflections.
Book1
ABCDEFGHI
1898-8.0186XYDeltaInflections:282
289710.061418.0889710.061418.08
389610.0614089510.00074-0.060661
489510.00074-0.060668928.752501-1.248240
589410.00074089010.87252.121
689310.0007408857.905478-2.967021
78928.752501-1.24824877-8.26952-16.1750
88918.7525010873-13.7147-5.445140
989010.87252.12872-8.814554.9001161
1088910.87250869-7.1091.7055440
1188810.87250868-21.769-14.661
1288710.87250867-21.05140.7176291
1388610.87250864-19.92341.1279820
148857.905478-2.96702851-36.3434-16.421
158847.9054780850-43.0764-6.732980
168837.9054780847-40.88142.1951
178827.9054780841-32.75148.130
188817.9054780840-36.2848-3.533431
198807.9054780826-34.08982.1951
208797.9054780824-27.45486.6350
218787.9054780823-14.487712.967150
22877-8.26952-16.175815-16.4877-21
23876-8.269520805-14.29272.1951
24875-8.269520804-43.7627-29.471
25874-8.269520800-74.6235-30.86080
26873-13.7147-5.44514798-58.078516.5451
27872-8.814554.900116794-57.56850.510020
28871-8.814550793-57.55350.0150
29870-8.814550791-67.5535-101
30869-7.1091.705544789-65.84351.711
31868-21.769-14.66788-65.73350.110
32867-21.05140.717629785-68.7385-3.0051
33866-21.05140784-66.50852.231
34865-21.05140782-49.858516.650
35864-19.92341.127982778-40.6379.221480
36863-19.92340777-92.0963-51.45921
37862-19.92340775-102.096-100
38861-19.92340771-97.36964.7266451
39860-19.92340770-108.554-11.18431
Sheet1
Cell Formulas
RangeFormula
I1I1=SUM(H2:H583)
E2:G583E2=FILTER(A1:C899,C1:C899<>0)
C2:C39C2=B2-B1
H3:H39H3=IF(SIGN(G3)<>SIGN(G2),1,0)
Dynamic array formulas.
 
Upvote 0
Thanks for the quick reply. What column would I add on to my chart to get the derivative and would I subtract that new column from column b? I'm not great with excel
 
Upvote 0
I've got it there in my reply. Column C is the 'derivative' of column B. You can see that C2 = B2-B1. So for each derivative you loose a row of data.

Your data set had a many records where there was no change for 5 or 6 rows. So I filtered that out in Columns E and F - hoping to smooth it out a bit. It didn't help much. You have noisy data.

You might try smoothing a bit, and then taking the derivative. Maybe C10 could be AVERAGE(B1:B10), and then drag that down to the bottom of your data. Then in D11 = C11-C10. Then graph the new C and D.
 
Upvote 0

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