Hello community,
I play with the Build-In-Fitting-Functions of my Origin Version 8.0.
While the fitting analysis two Problems/questions rises.
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a)
First I want to realize a linear fit (data: Attenuation over SQRT(Frequency)) in two different ways:
1) Go to Analysis --> Fitting --> Fit Linear
2) Go to Analysis --> Fitting --> Nonlinear Curve Fit --> Category Polynominal --> Function Line
Two different results I get:
1) f(x) = -0.36862 - 2.21595E-4 * x
2) f(x) = -0.37441 - 2.13699E-4 * x
Result 1) is the same I get using Excel for data fitting
What is the difference of both function/both ways?
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b)
Second, with same database I want to do a SQRT-Fit (data: Attenuation over Frequency).
2) Go to Analysis --> Fitting --> Nonlinear Curve Fit --> Category Polynominal --> Function Line --> Duplicate Function Line --> Modify Function to y = a + b * x^0.5 and fit.
Result is: f(x) = -0.36759 - 2.35614E-4 * SQRT(x)
Its totally different compared to a fit using Matlab. With Matlab I get Result 1) of a).
Where is my mistake...? I appreciate your help!
Thanks in advance!
Database:
Frequency SQRT(Frequency) Attenuation
1000000 1000 -0,61432
1,0692E6 1034,02328 -0,62924
1,13841E6 1066,96217 -0,64161
1,20761E6 1098,91419 -0,65305
1,27682E6 1129,96307 -0,66504
1,35725E6 1165,01177 -0,67603
1,45423E6 1205,91408 -0,68895
1,55121E6 1245,47385 -0,70021
1,64818E6 1283,81519 -0,71129
1,74516E6 1321,04421 -0,72326
1,84213E6 1357,25242 -0,73534
1,95818E6 1399,35108 -0,74832
2,0937E6 1446,96159 -0,76068
2,22921E6 1493,05467 -0,77336
2,36473E6 1537,76677 -0,78591
2,50024E6 1581,21505 -0,79838
2,65775E6 1630,26048 -0,81205
2,84168E6 1685,72728 -0,82632
3,0256E6 1739,42626 -0,83905
3,20953E6 1791,51638 -0,84988
3,39346E6 1842,13414 -0,86005
3,60724E6 1899,27265 -0,87282
3,86498E6 1965,95407 -0,88723
4,12271E6 2030,4468 -0,90129
4,38045E6 2092,95318 -0,91461
4,63819E6 2153,64616 -0,92722
4,89593E6 2212,67499 -0,93913
5,20436E6 2281,30677 -0,95254
5,56452E6 2358,9243 -0,96742
5,92469E6 2434,06802 -0,98214
6,28485E6 2506,96039 -0,99576
6,64501E6 2577,7924 -1,00891
7,06363E6 2657,74924 -1,02356
7,55246E6 2748,17457 -1,03934
8,0413E6 2835,71789 -1,05456
8,53013E6 2920,63836 -1,06959
9,01896E6 3003,15849 -1,08285
9,58713E6 3096,30914 -1,09881
1,02721E7 3205,01722 -1,11457
1,09571E7 3310,15717 -1,13064
1,16421E7 3412,05885 -1,14473
1,23272E7 3511,00423 -1,15857
1,30122E7 3607,23659 -1,17205
1,38319E7 3719,12427 -1,18758
1,47891E7 3845,66107 -1,20541
1,57463E7 3968,1649 -1,22413
1,67036E7 4086,99845 -1,24296
1,76608E7 4202,47309 -1,26121
1,87734E7 4332,82355 -1,28261
2,00726E7 4480,2404 -1,30589
2,13717E7 4622,95882 -1,32784
2,26709E7 4761,4013 -1,35013
2,39701E7 4895,93061 -1,37185
2,54802E7 5047,79043 -1,39715
2,72435E7 5219,5328 -1,42807
2,90069E7 5385,80143 -1,45885
3,07702E7 5547,08856 -1,48991
3,25335E7 5703,81678 -1,51908
3,4583E7 5880,73526 -1,55336
3,7054E7 6087,20155 -1,59574
3,9525E7 6286,89098 -1,63769
4,1996E7 6480,43006 -1,67756
4,44669E7 6668,35431 -1,71724
4,69379E7 6851,1258 -1,75726
4,98949E7 7063,63101 -1,80471
5,33478E7 7303,95888 -1,8567
5,68007E7 7536,62706 -1,9095
6,02537E7 7762,32438 -1,96125
6,37066E7 7981,64219 -2,01044
6,772E7 8229,21326 -2,06908
7,24065E7 8509,19806 -2,13568
7,7093E7 8780,25923 -2,19792
8,17795E7 9043,19926 -2,25999
8,6466E7 9298,70709 -2,31962
9,19131E7 9587,1303 -2,38887
9,84803E7 9923,72413 -2,46755
1,05048E8 10249,26992 -2,54334
1,11615E8 10564,78902 -2,62136
1,18182E8 10871,15451 -2,69058
1,24749E8 11169,11964 -2,76093
1,32608E8 11515,55849 -2,84466
1,41785E8 11907,35551 -2,93497
1,50962E8 12286,66527 -3,02417
1,60139E8 12654,61068 -3,11343
1,69316E8 13012,15583 -3,19597
1,79983E8 13415,76117 -3,29417
1,92438E8 13872,20932 -3,41071
2,04894E8 14314,10964 -3,51507
2,17349E8 14742,77038 -3,6193
2,29805E8 15159,31469 -3,72249
2,44282E8 15629,51966 -3,83953
2,61736E8 16178,25528 -3,98124
2,7919E8 16708,97971 -4,11834
2,96644E8 17223,35804 -4,25289
3,14098E8 17722,81358 -4,38565
3,31552E8 18208,57436 -4,51721
3,52439E8 18773,35993 -4,66383
3,76829E8 19412,09113 -4,83475
4,0122E8 20030,46483 -5,00017
4,2561E8 20630,3117 -5,16508
4,5E8 21213,20344 -5,32909
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Problems with Fitting Algorithm
Posted - 07/24/2014 : 07:18:05 AM
