How to calculate enrgy of a matrix

I am having a 2*2 matrix. say it is A=[1 2; 3 4]; how to calculate energy with this.

Answer 1

[Image Analyst]

What is your definition of energy? You could say that if the array is an image, the pixel values are energy already so you can just sum the array

energy = sum(A(:));

Or you can use the energy as defined from the gray level co-occurrence matrix of the array. From the help for graycoprops():

Calculate statistical properties of the GLCM.

stats = graycoprops(glcm)
stats = 

         Contrast: 2.8947
      Correlation: 0.0783
           Energy: 0.1191
      Homogeneity: 0.5658

Perhaps you have some other definition - I don't know. After you read this, please clarify your definition of energy.

[sakshi ahuja]

I am having a filter LL_LL of size 68*68 size. I have to calculate the statistical data: energy. So how can i do that.

[sakshi ahuja]

My target is to find the energy compaction ratio. For this i have to calculate approximated energy and energy of original signal.

[sakshi ahuja]

How can we prove that "the pixel values are energy".

[Salma Hassan]

what about the matrix which i want to compute the energy of it , is one vector

[Image Analyst]

I don't know what your vector represents. It might represent energy. Pixels are energy - just go back to first principles to work out the units.

(A watts /square meter) * (B square meters/pixel) * (C Joules/(Watt second)) * (D seconds exposure time) = Joules that are collected in a one pixel area during the exposure time. So gray levels is proportional to Joules.

[Salma Hassan]

my feature vector was extracted by Discrete wavelet transform (DWT) as the paper in this link http://www.biomedres.info/biomedical-research/computer-aided-diagnostic-cad-for-feature-extraction-of-lungs-in-chest-radiograph-using-different-transform-features.html