What does x(1,:) do in MATLAB ?

What does x(1,:) do in MATLAB ?

eg:

at = sqrt(Po)*exp(-0.5*(1+i*C)*(tau./t0).^(2*m)) 
a0 = fft(at(1,:));

what does at(1,:) do here ?

[Anil Chowdary Tummala]

Q1. What does x(1,:) do in MATLAB ?

Answer : It gives the first row of matrix 'x'

Q2. what does at(1,:) do here ?

Answer : it gives the first row of FFT coefficients of matrix 'at'

[Anil Chowdary Tummala]

Thank you very much

Answer 1

[Dr. Seis]

"a0" is the Fourier Transform of the first row of "at"

at(2,:) % gives the second row
at(3,:) % gives the third row (and so on)

at(:,1) % gives the first column (and so on)

[JIIT Bainwala]

thnx!

Answer 2

[Afissou ZONGO]

X(i*2,:) means

[Walter Roberson]

Take the current value of the variable i and multiply it by 2. Use the result as row indices to select entire rows of X.

The code shown does not require that i is a scalar or even a vector. It also does not require that the values in i are currently integer values, but if they are not then there is the risk that there could be an indexing error.

There are uncommon cases in which i would not necessarily have to be numeric, but you might never see that happen in practice.

Answer 3

[Sorabh Mahajan]

x = [x;i] meaining

[Walter Roberson]

[A;B] is defined as being vertcat(A, B) which in turn is defined as being the same as cat(2,A,B)

That is, [x;i] takes the existing array x, and tries to place a new row containing i at the bottom of it. With the x= assignment that becomes the new x. The effect is to add the content of i to the bottom of x.

Answer 4

[Antonio]

x(1:2,1)? meaning

[Steven Lord]

This performs "Indexing with Element Positions". In particular, "You can also reference multiple elements at a time by specifying their indices in a vector."