For loop in a for loop doesn't work

So I'm playing with audio data and I have created a script which downsamples an audio file. Now I'm trying to write a script that tries to recompose the original audio copying the value of the data lost with the downsampling. This is my script

prompt = 'Specific matrix ';
matrix = input(prompt); %audio matrix 1 column
prompt = 'Specific frequency destination ';
freqdest = input(prompt);
prompt = 'Specific frequency signal ';
frq = input(prompt);

sstep = freqdest/frq;
X=ones(length(matrix)*sstep,1); %creating the new matrix

for n=1:length(matrix) % n counter matrix total
    for m=0:sstep-1
        X(n+m)=matrix(n);
    end
end

The inside for

for m=0:sstep-1
          X(n+m)=matrix(n);
end

Seems not working at all. The script creates correctly the matrix with the right dimension but copy all the value of "matrix" in "X" without launch the script for every value. Why? Has someone a solution? Thanks

Answer 1

[Nico]

for n=1:length(matrix) % n counter matrix total
    for m=0:sstep-1
        X(n+m+h)=matrix(n);
    end
    h=h+sstep-1;
end

This is the right loop

Answer 2

[M]

You should be careful when manipulating matix.

M(i,j)

returns the value of the ith row and jth column of the matrix.

In your example you just give one argument to your matrices.

[Nico]

Yeah because my matrix has only one column. I have tried also with ,1 but it doesn't work

[Walter Roberson]

That is okay. The comments indicate that it is a vector with one column.

Answer 3

[Walter Roberson]

            X(n+m)=matrix(m);

perhaps? You were always copying the same value, matrix(n)

[Nico]

yeah because the internal loop copy the same value for sstep times but when it ends it should go through the next n values, but it doesn't

Answer 4

[Jan]

Use the debugger to find out, what's going on: Set a breakpoint inside the loop and step through the code line by line observing the values of the counters.

for n=1:length(matrix) % n counter matrix total
  for m=0:sstep-1
      X(n+m)=matrix(n);
  end
end

Note that e.g. x(2) is assigned by n=1 and m=1 and by n=2 and m=2. Perhaps you want:

X = repmat(matrix, 1, sstep)

or

X = repelem(matrix, 1, sstep)

or perhaps the same with matrix(:) or a transposition.

[Nico]

Oh I found the bug thanks to your phrase "n=1 and m=1 and by n=2 and m=2" It's my logic error, I will fix it and post the correct code