Meaning of the symbol in the equation

Please can someone tell me what the ||equation||2 symbol denotes in the equation given the link.... Please do reply.... Please can anyone help me to code that line... i dont know what that symbol ||equation||2 stands for..... Please do reply what is the meaning of

||y(x,n)......||2

Please do reply.....

Answer 1

[Jan]

you are looking at the square of a vector norm:

|v|||^2 = sqrt( v_1^2 + v_2^2 + ... + v_n^2 ) = v_1^2 + v_2^2 + ... + v_n^2

[Elysi Cochin]

thank u sir...