Meaning of x = X(training(c,1),:);

Kindly explain me the meaning of X (training(c,1),:)? what is the significance of : in matlab commands?

Answer 1

[Stephen23]

Why not use the power of the internet to learn how MATLAB works? I used [an internet search engine] to search for "MATLAB colon" and the very first result was this very informative page:

http://www.mathworks.com/help/matlab/ref/colon.html

At the top of the page is written "The colon is one of the most useful operators in MATLAB", and just a few lines down the page I found this example:

A(i,:)        is the ith row of A.

which matches your example. After reading that page we learn that the line

X(training(c,1),:)

uses indexing to return the training(c,1)-th rows of the variable X. Alternatively you can think of the colon as meaning "all columns" of X (because it is used as the column index).

Here is a simple example:

>> X = [1,2;3,4] % define a matrix
X =
   1   2
   3   4
>> X(1,:) % pick the first row and all columns
ans =
   1   2