# How do the initial parameter values "start" work in the Three-Parameter Weibull Distribution?

4 ビュー (過去 30 日間)
Mustafa Vural 2020 年 5 月 12 日
コメント済み: Rik 2020 年 12 月 7 日
Trying to estimate a Three-Parameter Weibull Distribution. In the scripture of Matlab, there is given the following execution:
rng('default') %For reproducibility
data = wblrnd(1,1,[1000,1]) + 10;
custompdf = @(x,a,b,c) (x>c).*(b/a).*(((x-c)/a).^(b-1)).*exp(-((x-c)/a).^b);
opt = statset('MaxIter',1e5,'MaxFunEvals',1e5,'FunValCheck','off');
params = mle(data,'pdf',custompdf,'start',[5 5 5],'Options',opt,'LowerBound',[0 0 -Inf],'UpperBound',[Inf Inf min(data)])
I dont really understand, how the numbers after 'start' work? What relationship do the numbers have to the scale, shape and location parameters? Days spent searching for an answer.. The following picture demonstrates my problem:
##### 1 件のコメント表示非表示 なし
Rik 2020 年 12 月 7 日
Please do not delete your question. If you feel this is a beginner question: there are many beginners, so be nice to them. They might come across your question and learn from it.
I made a capture so people can revert your edit if you attempt to vandalize your question.

サインインしてコメントする。

### 採用された回答

Harsha Priya Daggubati 2020 年 5 月 15 日
Hi,
The 'start' argument in mle method is used to specify intial parameter values to the custom probability distribution function specified by the user. The value of start is also constrained such that it lies between Upper and Lower bounds specified.
In the highlighted case, due to the change of wiebull distribution parameters I guess the min(data) is less than the values of start specified. Thus leading the constraint to fail.
##### 2 件のコメント表示非表示 1 件の古いコメント
Harsha Priya Daggubati 2020 年 5 月 22 日
The value of the start is used to give initial values for the parameters in your probability distribution function i.e custompdf. I didnot understand what do you mean by shape and scale parameters.

サインインしてコメントする。

### カテゴリ

Find more on Weibull Distribution in Help Center and File Exchange

R2019b

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by