How do I plot logarithmic error?
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I have data that I want to plot on a log y-scale because it's not linear. When I plot the error, the bars are not of equal length (lower error looks larger) because of the log y-scale. How do I transform the error so it becomes the relative error and I get error bars of equal lengths above and below the datapoints?
I want to plot the error as a shaded area around the main data, so I need not plot a line above and below the main data. How do I calculate these two lines?
I don't calculate the logarithm of my data, I just plot it, and then change the y-axis through:
set(gca,'YScale','log');
Edit:
For clarity a figure of the problem. The dotted lines is the 'data + error', and the 'data - error'. Because of the log scale, the error seems way lager for the 'data - error', eventhough the error margin is equal above and below the data line. How do I transform the error so it has an equal distance between the error above and below the data line? I Hope this is more clear now.
data = [1.0 1.4 1.5 2.6 1.9 1.9 3.6 4.3 9.5 9.2];
error = [1.2 1.1 1.4 2.0 1.5 1.2 2.2 2.6 0.6 0.7];
dataPlus = data + error;
dataMin = data - error;
采纳的回答
J. Alex Lee
2020-8-18
In log space, spacing is multiplicative, not additive, so you want to express your top and bottom curves as multiples of your base curve
clc;
close all;
clear;
data = [1.0 1.4 1.5 2.6 1.9 1.9 3.6 4.3 9.5 9.2];
err = [1.2 1.1 1.4 2.0 1.5 1.2 2.2 2.6 0.6 0.7];
% above
dataPlus = data + err;
dataPlusMult = dataPlus./data;
% below
dataMinus = data ./ dataPlusMult;
figure(1); cla; hold on;
plot(data,'-')
plot(dataPlus,'--')
plot(dataMinus,'--')
set(gca,'YScale','log')
2 个评论
Niek Blikslager
2020-8-19
J. Alex Lee
2020-8-19
Glad it helps.
Just to comment that your plot no longer reflects what you actually wanted to convey, if what you wanted to convey is data +/- err.
更多回答（1 个）
J. Alex Lee
2020-8-17
0 个投票
use the log10() function? The question isn't super clear...
2 个评论
Niek Blikslager
2020-8-18
J. Alex Lee
2020-8-18
the plot of the data is what it is, you can't change how it looks without changing the error values themselves...
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