What does normc function do?

Hi

Can someone tell me what does normc function do? Well ... it normalizes data in each column but to what range ([0,1]?) ? I read the description but I can't fully understand.

Thanks.

Answer 1

[Star Strider]

It normalises the sum of the squares of the elements in each column to have a value of 1.

To illustrate:

M = randi(20,5,5);          % Create Random Matrix
Mnc = normc(M);             % Call ‘normc’
Ssq = sum(Mnc.^2);          % Column Sum-Of-Squares

[Insos]

Do you know the math behind the function?

[Star Strider]

It’s fairly short. Type:

type normc.m

in the Command Window to see how it works. (It’s copyrighted, so I can’t copy and post it here.)

[Insos]

One last question ... is there any advantage of doing normalization with normc instead of normalizing data between [0,1] with the min and max value?

[Star Strider]

There is, because normc retains the relative magnitudes of the data in each column with respect to the length of the vector they describe. Normalising between min and max destroys those relationships.

How you normalise them depends on what you want to do with your data, but if your data span a vector space and you want to preserve the relationships between the vector components, normc (or normr) are your only options.