Fitdist gives wrong answer
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fitdist is givin me mu of 6.43686 with this code. Am i doing something wrong. I'm trying to get mu and sigma values to compare this data with log normal distribution
Add=16
%%info given in question 4
River_flood_level=[516 678 802 683 491 582 625 531 451 726 652 556 470 570 774 670 432 604 881 707 735 614 698 403 548 504 758 1000 419];
River_flood_level=River_flood_level+Add;
%%solution of question 4
fitdist(River_flood_level.','Lognormal')
1 个评论
Why do you think the result is incorrect? What are you expecting mu to be?
The fitted distribution looks pretty reasonable given the limited amount of data provided.
Add=16;
%%info given in question 4
River_flood_level=[516 678 802 683 491 582 625 531 451 726 652 556 470 570 774 670 432 604 881 707 735 614 698 403 548 504 758 1000 419];
River_flood_level=River_flood_level+Add;
%%solution of question 4
p = fitdist(River_flood_level.','Lognormal');
figure
histogram(River_flood_level,'Normalization','pdf')
hold on
plot(400:1200,pdf(p,400:1200))
采纳的回答
The μ and σ values are in log units. Calculatee their exponentials —
Add=16
%%info given in question 4
River_flood_level=[516 678 802 683 491 582 625 531 451 726 652 556 470 570 774 670 432 604 881 707 735 614 698 403 548 504 758 1000 419];
River_flood_level=River_flood_level+Add;
%%solution of question 4
df = fitdist(River_flood_level.','Lognormal')
Mean = exp(df.mu)
Sigma = exp(df.sigma)
figure
hf = histfit(River_flood_level.', 10, 'Lognormal');
hold on
Line = findobj(hf,'Type','line');
ymu = interp1(Line.XData, Line.YData, exp(df.mu));
plot(exp(df.mu)*[1 1], [0 ymu], ':r', 'LineWidth',3)
hold off
Ax = gca;
Ax.XTickLabelRotation = 60;
.
6 个评论
Emmeirrt
2024-1-6
Star Strider
2024-1-6
As always, my pleasure!
I have not worked with lognormal distrbutions in a while (although all physiological parameters are lognormally distributed) so I had to rediscover that.
Corrected —
Add=16
%%info given in question 4
River_flood_level=[516 678 802 683 491 582 625 531 451 726 652 556 470 570 774 670 432 604 881 707 735 614 698 403 548 504 758 1000 419];
River_flood_level=River_flood_level+Add;
%%solution of question 4
df = fitdist(River_flood_level.','Lognormal')
m = exp(df.mu + df.sigma^2/2)
nu = exp(2*df.mu+df.sigma^2)*(exp(df.sigma^2)-1);
figure
hf = histfit(River_flood_level.', 10, 'Lognormal');
hold on
Line = findobj(hf,'Type','line');
ymu = interp1(Line.XData, Line.YData, m);
plot([1;1]*m, [0;1]*ymu, '--r', 'LineWidth',2)
hold off
Ax = gca;
Ax.XTickLabelRotation = 60;
.
Emmeirrt
2024-1-29
Star Strider
2024-1-29
As always, my pleasure!
No worries!
Thank you for the follow-up (and for Accepting my Answer).
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