Reorganizing a vector in c++ - c++

Question

I'd like to preface this question with the fact that I am very inexperienced when it comes to coding, so the solution to this problem could be much easier than what I have been trying. I have a vector 'phas' defined as vector<float> phase; that has 7987200 elements and I want to rearrange this vector into 133120 vectors of 60 elements (called line2 defined as vector<long double> line2;). Each vector of 60 should then be placed one after the other in a vector of vectors 'RFlines2' defined as vector< vector<long double> > RFlines2;and RFlines2.resize(7987200);. I want to fill each of the 60 element vectors with elements of 'phas' separated by 128. for example, the first vector of 60 elements would be filled with phas[0], phas[128], phas[256], ... phas[7680]. The second vector of 60 would then be filled with phas[1], phas[129], phas[257], ... phas[7681],...etc. My current code is as follows:
for(int x = 0; x<133120; x++){
if((x == 128 || x == 7680+128 || x == (7680*a)+128)){
x = 7680*a;
a = a + 1;
}
int j = x;
for(int i = 0; i<60;i++){
line2.pushback(i);
line2[i] = phas[j];
j = j + 128;
}
cout<<"This is x: "<<x<<endl;
RFlines2[x] = line2;
line2.clear();
}
however, after 128 iterations of the outter loop (128 vectors of 60 have been created and 7680 elements from phas have been used), I would need the x value to jump to 7680 to avoid putting elements from phas that have already been used into the next vector of 60 since when x = 128 the first element of the next vector of 60 would be phase[128], which was already used as the 2nd element of the first vector of 60. And then after another 128 x iterations, I would need the x value to jump to 15,360 and so on. The code above is my latest attempt, but when I try to do the fftw on each vector of 60 in RFlines2 as follows:
int c = 0;
for(int x = 0; x < 133120; x++){
//cout<<x<<endl;
fftw_plan p2;
inter = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * W);
outter = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * W);
/* cast elements in line to type fftw_complex */
for (int i = 0; i <60; i++) {
//cout<<i<<endl;
//inter[i][0] = phas[i];
//inter[x][0] = zlines[x];
inter[i][0] = RFlines2[x][i];
inter[i][1] = 0;
}
p2 = fftw_plan_dft_1d(60, inter, outter, FFTW_FORWARD, FFTW_ESTIMATE);
fftw_execute(p2);
//inter[x][0].clear();
for(int u = 0; u<60;u++){
if(u == 0){
cout<<' '<<outter[0][0]<<' '<<c++<<endl;
}
}
fftw_free(inter);
fftw_free(outter);
fftw_destroy_plan((p2));
}
the program crashes after displaying outer[0][0] 128 times. Any ideas how to fix this? Also, let me know if anything that I said doesn't make sense and I'll try to clarify. Thanks in advance!
-Mike

Answer 1

I don't know why your code crashes, because I can't see the whole code here. But I'm going to suggest a way to scatter your data and manage your vectors.
(There is an important caveat though: you should not be using vectors (at least not vectors of vectors) for this task; you are better off using 1D vectors and managing the 2D indexing yourself. But this is a performance thing, and does not impact correctness.)
This is how I suggest you fill your RFLines2: (I have not tried this code, so it may not work.)
// first, build the memory for RFLines2...
vector<vector<long double>> RFLines2 (133120, vector<long double>(60));
// assuming a "phase" vector...
for (unsigned i = 0; i < 7987200; ++i)
{
unsigned const row = (i / (128 * 60)) * 128 + (i % (128 * 60)) % 128;
unsigned const col = (i % (128 * 60)) / 128;
RFLines[row][col] = phase[i];
}
You won't need the line2 intermediate this way.
The rest of the code "should" work. (BTW, I don't understand the inner for loop on u at all. What were you trying to do there?)