Databases
StackOverflow2013
Postsdbo
POFinding the elbow point of a curve in a stable way?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POFinding the elbow point of a curve in a stable way?
    primarykey
    data
    text
    <p>I am aware of the existence of <a href="https://stackoverflow.com/questions/4033821/using-a-smoother-with-the-l-method-to-determine-the-number-of-k-means-clusters">this</a>, and <a href="https://stackoverflow.com/questions/2018178/finding-the-best-trade-off-point-on-a-curve">this</a> on this topic. However, I would like to finalize on an actual implementation in Python this time. </p> <p>My only problem is that the elbow point seems to be changing from different instantiations of my code. Observe the two plots shown in this post. While they appear to be visually similar, the value of the elbow point changed significantly. Both the curves were generated from an average of 20 different runs. Even then, there is a significant shift in the value of the elbow point. What precautions can I take to make sure that the value falls within a certain bound?</p> <p>My attempt is shown below:</p> <pre><code>def elbowPoint(points): secondDerivative = collections.defaultdict(lambda:0) for i in range(1, len(points) - 1): secondDerivative[i] = points[i+1] + points[i-1] - 2*points[i] max_index = secondDerivative.values().index(max(secondDerivative.values())) elbow_point = max_index + 1 return elbow_point points = [0.80881476685027154, 0.79457906121371058, 0.78071124401504677, 0.77110686192601441, 0.76062373158581287, 0.75174963969985187, 0.74356408965979193, 0.73577573557299236, 0.72782434749305047, 0.71952590556748364, 0.71417942487824781, 0.7076502559300516, 0.70089375208028415, 0.69393584640497064, 0.68550490458450741, 0.68494440529025913, 0.67920157634796108, 0.67280267176628761] max_point = elbowPoint(points) </code></pre> <p><img src="https://i.stack.imgur.com/8dVct.png" alt="enter image description here"> <img src="https://i.stack.imgur.com/KK6v5.png" alt="enter image description here"></p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USLegend
    plurals
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POFinding the elbow point of a curve in a stable way?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POFinding the elbow point of a curve in a stable way?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COJust a small sidenote: You shouldn't use a defaultdict for a function with a default value, because then a dictionary entry will be created at `yourDefaultDict[i]` for all values `i` you query. Here I can't see an issue with it.
      singulars
      1. POFinding the elbow point of a curve in a stable way?
      1. USninjagecko
    2. CO@ninjagecko: Oh! You're right! I will fix it my version. Thank you for pointing it out.
      singulars
      1. POFinding the elbow point of a curve in a stable way?
      1. USLegend
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload