Knee point in logistic-like curve

Hi, I have a curve that looks like a logistic function (data array below):

I need to find the knee where it starts to grow, which would be around ~75, but I can’t seem to be able to do it. I’ve tried all the combinations of the curve, direction parameters to no avail.

Is kneed capable of doing this?

Cheers

[array([ 1.,  2.,  3.,  4.,  5.,  6.,  7.,  8.,  9., 10., 11., 12., 13.,
       14., 15., 16., 17., 18., 19., 20., 21., 22., 23., 24., 25., 26.,
       27., 28., 29., 30., 31., 32., 33., 34., 35., 36., 37., 38., 39.,
       40., 41., 42., 43., 44., 45., 46., 47., 48., 49., 50., 51., 52.,
       53., 54., 55., 56., 57., 58., 59., 60., 61., 62., 63., 64., 65.,
       66., 67., 68., 69., 70., 71., 72., 73., 74., 75., 76., 77., 78.,
       79., 80., 81., 82., 83., 84., 85., 86., 87., 88., 89., 90., 91.,
       92., 93., 94., 95., 96., 97., 98.]), array([2.00855493e-45, 1.10299045e-43, 4.48168384e-42, 1.22376580e-41,
       5.10688883e-40, 1.18778110e-38, 5.88777891e-35, 4.25317895e-34,
       4.06507035e-33, 6.88084518e-32, 2.99321831e-31, 1.13291723e-30,
       1.05244482e-28, 2.67578448e-27, 1.22522190e-26, 2.36517846e-26,
       8.30369408e-26, 1.24303033e-25, 2.27726918e-25, 1.06330422e-24,
       5.55017673e-24, 1.92068553e-23, 3.31361011e-23, 1.13575247e-22,
       1.75386416e-22, 6.52680518e-22, 2.05106011e-21, 6.37285545e-21,
       4.16125535e-20, 1.12709507e-19, 5.75853420e-19, 1.73333796e-18,
       2.70099890e-18, 7.53254646e-18, 1.38139433e-17, 3.60081965e-17,
       8.08419977e-17, 1.86378584e-16, 5.36224556e-16, 8.89404640e-16,
       2.34045104e-15, 4.72168880e-15, 6.84378992e-15, 2.26898430e-14,
       3.10087652e-14, 2.78081199e-13, 1.06479577e-12, 2.81002203e-12,
       4.22067092e-12, 9.27095863e-12, 1.54519738e-11, 4.53347819e-11,
       1.35564441e-10, 2.35242087e-10, 4.45253545e-10, 9.78613696e-10,
       1.53140922e-09, 2.81648560e-09, 6.70890436e-09, 1.49724785e-08,
       5.59553565e-08, 1.39510811e-07, 7.64761811e-07, 1.40723957e-06,
       4.97638863e-06, 2.12817943e-05, 3.26471410e-05, 1.02599591e-04,
       3.18774179e-04, 5.67297630e-04, 9.22732716e-04, 1.17445643e-03,
       3.59279384e-03, 3.61936491e-02, 6.39493416e-02, 1.29304829e-01,
       1.72272215e-01, 3.46945901e-01, 5.02826602e-01, 6.24800042e-01,
       7.38412957e-01, 7.59931663e-01, 7.73374421e-01, 7.91421897e-01,
       8.29325597e-01, 8.57718637e-01, 8.73286061e-01, 8.77056835e-01,
       8.93173768e-01, 9.05435646e-01, 9.17217910e-01, 9.19119179e-01,
       9.24810910e-01, 9.26306908e-01, 9.28621233e-01, 9.33855835e-01,
       9.37263027e-01, 9.41651642e-01])]

[arvkevi]

Sure, @Gabriel-p – I’ve been meaning to make proper documentation for this repo for a year now… I hope this explanation will do, for now.

When online=False the first knee point identified is returned regardless of whether it’s the local maxima on the difference curve or the global maxima. So the algorithm stops early. When online=True, kneed runs in online mode and “corrects” itself by continuing to overwrite any previously identified knees.

Here’s a quick example to show the usage of the parameter.

online=False:

from kneed import KneeLocator
y = [0, 1.0, 1.5, 1.8, 1.9, 2.0, 3.5, 5.0, 7.0, 9.0, 9.5, 9.75, 9.9, 10]
kl = KneeLocator(range(len(y)), y, curve="concave", direction="increasing", online=False)
kl.plot_knee_normalized()

online=True:

kl = KneeLocator(range(len(y)), y, curve="concave", direction="increasing", online=True)
kl.plot_knee_normalized()

[arvkevi]

Hey @Gabriel-p sorry for the delay, I have a working branch and an open PR that identifies the knee in your example at x = 73 using the following arguments:

kl = KneeLocator(x, y, curve="convex", direction="increasing", online=True)

You can try installing from source for now until I get this merged and cut a new release.