plot SEM error bars

hi everyone, i have 2 column such as

X=[ -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10]

Y=[0.9996 1.0000 0.9772 0.8978 0.6916 0.3253 0.0680 0.0091 0.0089 0.0088 0.0098 0.0119]

i want to plot SEM error bars using errorbar function,but when i calculate the SEM it only gives me one value and errobar function show this error:

'X, Y and error bars must all be the same length'

can you please help me with that.

SEM=std(data)./sqrt(length(data))

thank you

Answer 1

[Star Strider]

If your ‘data’ matrix variables are in columns and ‘Y’ is the mean, you need to calculate the ‘SEM’ across the columns of ‘data’:

SEM = std(data,2)./sqrt(size(data,2));

You calculate the mean the same way:

Y = mean(data,2);

Note: This is a guess, since I do not have your data.

[best16 programmer]

thank you for the answer my data column is

data=[-79.6696 -73.4101 -80.6085 -72.3433 -70.2953 -77.0140 -75.6808 -75.9423]

[Star Strider]

My pleasure.

Your ‘data’ vector has only 8 elements. Your other vectors have 12. Your ‘data’ vector will produce only 1 value if you calculate the standard deviation over the column, and the standard deviation is 0 for single values (calculating the standard deviation row-wise, across the columns).

There is no solution to your problem with the information you have provided.

[best16 programmer]

thank you again,can you please show me some example for this type of operation

[Star Strider]

My pleasure.

This is one example (using your ‘X’ and ‘Y’ vectors):

X = [ -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10]';
Y = [0.9996 1.0000 0.9772 0.8978 0.6916 0.3253 0.0680 0.0091 0.0089 0.0088 0.0098 0.0119]';

data = Y + 0.1*randn(12, 8);                        % Create (12x8) Data Array

data_mean = mean(data,2);                           % Mean Across Columns
data_SEM = std(data,[],2)/sqrt(size(data,2));       % SEM Across Columns

figure(1)
errorbar(X, data_mean, data_SEM)
grid
axis([-130  0    ylim])