# error in std for 3d matrix

3 views (last 30 days)
Anastasia on 12 Dec 2016
Commented: Guillaume on 13 Dec 2016
Hey guys!
I am trying to find the std of a 3D matrix, where size(X) is 207 x 201 x 34. Since I must reshape to find std, I am using this formula: std(reshape(X,1,207*201*34)).
And I obtain this error: Error in std (line 31) y = sqrt(var(varargin{:}));
When I look at the syntax, I thought of using std(reshape(X,1,207*201*34), 0, 3), where 3 is for 3D, however I still obtain the same error.
What I am missing?
Thank you very much in advance!
##### 2 CommentsShow 1 older commentHide 1 older comment
Anastasia on 13 Dec 2016
Edited: Anastasia on 13 Dec 2016
Hello, this is the full text of the error message:
Error using var (line 58) First argument must be single or double.
Error in std (line 31) y = sqrt(var(varargin{:}));
Error in Code3D (line 27) th=mean(mean(mean(X))) + std(reshape(X,1,207*201*34));
Is the problem that X is nor single nor double, but 207*201*34? How can I fix that?
Thank you!

try std(x(:))
Anastasia on 13 Dec 2016
Hello! Thank you for your answer but I obtain the same error...

Guillaume on 13 Dec 2016
Error: First argument must be single or double
Well, clearly, your first argument (a transform of X) is not single or double. So what is:
class(X)
If it's an integer type:
Xdouble = double(X);
th = mean(Xdouble(:)) + std(Xdouble(:));
##### 2 CommentsShow 1 older commentHide 1 older comment
Guillaume on 13 Dec 2016
Without context it's impossible to say if it's correct or not. Certainly, if you want the standard deviation of your integers, you have to convert them to double. If an integer result is then required, you can convert the output back to uint16 (with the loss of precision that it entails).