Re: [eigen] FFT question

```Should be better now.

On 02/16/2010 11:49 AM, Mark Borgerding wrote:
```
It works when I use the raw pointer methods of FFT. It is something in the Eigen matric functions. I should have a fix in the next day or so.
```
-- Mark

Trevor Irons wrote:
```
```Mark and others:

```
I'm trying to get the KISS FFT working for me, but am struggling a little with the Real to Complex and back case. I suspect I'm misusing it somehow, I based this off the tests. The Complex to Complex fwd and inv (Full Spectrum) are working with similar logic.
```
```
The forward operation seems to be accurate, but how do I do the inverse on 1/2 spectrum. If I don't remove the flag, I get a lot of errors at runtime (compiles fine):
```
g++ on 64 bit linux
```
*** glibc detected *** ./min: free(): invalid next size (normal): 0x0000000000da6790 ***
```======= Backtrace: =========
/lib/libc.so.6[0x7fc8a700cdd6]
/lib/libc.so.6(cfree+0x6c)[0x7fc8a701174c]

```
If I do remove the flag, thinking that maybe since the buffer is double, it will know it is a complex to real transform, but the answer is wrong.
```
If a do a full spectrum all is happy.

```
What am I doing wrong? If possible I'd like to just use the 1/2 spectrum. Thanks for any insight, really glad to have this out of the box like this.
```
#include "Eigen/Core"
#include "unsupported/Eigen/FFT"
#include <complex>

typedef std::complex<double> Complex;

using namespace Eigen;
using namespace std;

int main() {
FFT<double> fft;
double dt(1e-3);
VectorXd timeseries(200);
VectorXcd fd(200);

for (int i=0; i<200; ++i) {
timeseries[i] = std::sin((double)(i)*dt*95.);
}
fft.SetFlag(fft.HalfSpectrum );
fft.fwd(fd, timeseries);
VectorXd out;

// faults if I don't remove, wrong answer if I do
fft.ClearFlag(fft.HalfSpectrum );
fft.inv(out, fd);

for (int i=0; i< out.size(); ++i) {
cout << timeseries[i] << "\t" << out[i] << endl;
}
}
```
```

```
```

```

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