Standard deviation: error because variable is of type double

I've created a 30 by 15 array of random numbers with mean M and standard deviation sd. I've then scaled the values from 0 to 1 because I want to show the matrix v using imshow, so I want the range to be from 0 to 1. Here is my code:

%create array of random numbers v = randn(30,15)*sd + M; %scale minimum = min(min(v)); maximum = max(max(v)); v = (v-minimum)/maximum;

I then want to find the new standard deviation and mean. To find the mean, I use:

Mean = mean(mean(V));

To find the standard deviation, I have used this code:

v = reshape(30*15, 1); standard_deviation = std(v);

Please tell me if there is a better way to get the standard deviation of ALL the numbers in a matrix, without reshaping to make it into a vector. When I use the above code, matlab throws an error: Undefined function 'sdt' for input arguments of type 'double'. Why is this? v is a vector so I can't see the problem with finding the standard deviation.

Thanks

Answer 1

[yonatan gerufi]

Hi Anna,

you can use

 std2(matrix)
 mean2(matrix)

functions instead.

your code did work for me,

v = randn(30,15)*sd + M;
minimum = min(min(v));
maximum = max(max(v));
v = (v-minimum)/maximum;
Mean = mean(mean(v)); 
v = reshape(v,30*15, 1);
standard_deviation = std(v);

and that's it. good luck!

Answer 2

[Adam]

std( v(:) )

works for any dimensionality of v

Answer 3

[Image Analyst]

To get the mean and sd

theMean = mean(v(:)); % Works always.
theMean = mean2(v);  % Only if you have the Image Processing Toolbox
sd = std(v(:));  % Cast v to double if it's uint8 (like from an image).

To show the array, there is no need to scale to the range 0-1 , simple use []:

imshow(v, []);  % Require the Image Processing Toolbox (which you say you have).