FFT Why the flag and the array are not changed？

[Eagle_Lu]

---

ROOT Version: Not Provided
Platform: Not Provided
Compiler: Not Provided

---

here is my code：

int kind[0]=1;//DCT-II - kind=1
  double in[10]={1,2,3,4,5,6,7,8,9,10};
  double out[10]={};
  TFFTComplex *fft = new TFFTComplex(10,0);
  fft->Init("EX",-1,kind);//flag ="M"  sign=FFTW_FORWARD -1;    backward +1
  fft->SetPoints(in);
  fft->TFFTComplex::Transform(); //fplan not 0
  fft->TFFTComplex::GetPoints(in,"kFALSE");
  int a =fft->TFFTComplex::GetSize();
  cout <<"fTotalSize= "<< a << endl;//  10
  int b =fft->TFFTComplex::GetNdim();
  cout <<"fNdim= "<< b << endl;//       1
  int c =fft->TFFTComplex::IsInplace();
  cout <<"fout= "<< c << endl;//fout---bool     1       already changed
  int *d =fft->TFFTComplex::GetN();
  cout <<"fn= "<< *d << endl;//         10
  int e =fft->TFFTComplex::GetSign();
  cout <<"fsign= "<< e << endl;//       -1      already changed
  int f =fft->TFFTComplex::MapFlag();
  cout <<"flag= "<< f << endl;//        0(默认构造函数)*********flag***need change************
  char *g =fft->TFFTComplex::GetType();
  cout <<"getType= "<< g << endl;//     C2CBackward     prove (fsign is -1)
  //char *q =fft->TFFTComplex::GetTransformFlag();
  //cout <<"fFlags="<< q << endl;
  for (int i=0;i<10;i++)
  {cout << "i= "<< i <<"        in[i]= "<< in[i] <<endl;}//******need change*****************
   for (int i=0;i<10;i++)
  {cout << "i= "<< i <<"        out[i]= "<< out[i] <<endl;}

the output is：

fTotalSize= 10
fNdim= 1
fout= 1
fn= 10
fsign= -1
flag= 0
getType= C2CBackward
i= 0    in[i]= 1
i= 1    in[i]= 2
i= 2    in[i]= 3
i= 3    in[i]= 4
i= 4    in[i]= 5
i= 5    in[i]= 6
i= 6    in[i]= 7
i= 7    in[i]= 8
i= 8    in[i]= 9
i= 9    in[i]= 10
i= 0        out[i]= 0
i= 1        out[i]= 0
i= 2        out[i]= 0
i= 3        out[i]= 0
i= 4        out[i]= 0
i= 5        out[i]= 0
i= 6        out[i]= 0
i= 7        out[i]= 0
i= 8        out[i]= 0
i= 9        out[i]= 0

So I don’t know why the flag and the array in[] are not change？

[StephanH]

The best is to compile such examples. To compile and execute something in root, put it in a file and a function that have the same name. I posted the fixed code below, and this one you would put into testFFT.cxx.

If you did that, you could execute it as root.exe testFFT.cxx+. The + tells ROOT to compile it first, and execute afterwards. If you did that, you would have seen a couple of errors in your example.

This is what works for me now:

void testFFT() {
  int kind[1] = {1};//DCT-II - kind=1
  double in[10]={1,2,3,4,5,6,7,8,9,10};
  double out[10]={};
  TFFTComplex *fft = new TFFTComplex(10, false);
  fft->Init("EX",-1, kind);//flag ="M"  sign=FFTW_FORWARD -1;    backward +1
  fft->SetPoints(in);
  fft->Transform(); //fplan not 0
  fft->GetPoints(out, false);
  cout <<"fTotalSize= "<< fft->GetSize() << endl;//  10
  cout <<"fNdim= "<< fft->GetNdim() << endl;//       1
  cout <<"fout= "<< fft->IsInplace() << endl;//fout---bool     1       already changed
  int *d =fft->GetN();
  cout <<"fn= "<< *d << endl;//         10
  cout <<"fsign= "<< fft->GetSign() << endl;//       -1      already changed
//  int f =fft->MapFlag("EX");
//  cout <<"flag= "<< f << endl;//        0*********flag***need change************
  cout <<"getType= "<< fft->GetType() << endl;//     C2CBackward     prove (fsign is -1)
  //char *q =fft->TFFTComplex::GetTransformFlag();
  //cout <<"fFlags="<< q << endl;
  for (int i=0;i<10;i++)
  {cout << "i= "<< i <<"        in[i]= "<< in[i] <<endl;}//******need change*****************
   for (int i=0;i<10;i++)
  {cout << "i= "<< i <<"        out[i]= "<< out[i] <<endl;}
}

Some comments:

• When you call a function, don’t mention the name of the class. This is resolved automatically by C++.
• MapFlag is an internal function that you cannot call from the outside. I therefore commented it out.
• When you were “getting” the points, you put them in in instead of out.

[Eagle_Lu]

Thanks for your reply and comments! I know how to display the flag now.But I don’t know how to display the array that being transformed ,I can just show the original array.As you can see ,the array in[] didn’t change!!
This is my changed code:

This is the output:

[StephanH]

This is because you did not understand the difference between a boolean and a string.

May I first say again that it’s better to call functions without the class name

fft->GetPoints()

instead of

fft->TFFTComplex::GetPoints()

The latter might lead to surprising results or crashes if the fft pointer does not point to an FFTComplex object. In this case, it’s ok.

Your problem now is calling this function with fromInput = false:

void TFFTComplex::GetPoints(Double_t *data, Bool_t fromInput) const

What you do is to call like

GetPoints(data, <string>)

which passes the address of a string into the function. If you convert this to a Boolean (Wikipedia link), it is interpreted as true, because such an address is never 0. What you have to to is to call as:

GetPoints(data, false)

Like this, it is really interpreted as false, and the output array will be copied into your array.