title: Allocation memory error with dft_c2r_2d & FFTW_PRESERVE_INPUT
body: <p>I want to do a ‘complex_to_real’ transformation, it means, the IFFT. I realised that I need to preserve the inputs of the transformation for a later use, so I add to the plan of the ‘dft’ the flag : “PRESERVE_INPUT”. </p>
  
  <p>After adding this flag I become with a problem in compilation time , it goes to ‘dbgmalloc.c’, that means that it should be a allocation memory problem, but I didn’t change anything, and without the new flag it worked properly.</p>
  
  <p>Can you give me some hints?</p>
  
  <pre><code>    // IFFT ( U1,U2 --&gt; u1,u2)
      //----IFFT-----
      double *u1 = (double*) malloc(sizeof(double)*N_fft);
      double *u2 = (double*) malloc(sizeof(double)*N_fft);
      fftw_plan p3;
      fftw_plan p4;
  
      p3 = fftw_plan_dft_c2r_2d(alto, ancho, U1, u1, FFTW_ESTIMATE|FFTW_PRESERVE_INPUT);
      p4 = fftw_plan_dft_c2r_2d(alto, ancho, U2, u2, FFTW_ESTIMATE|FFTW_PRESERVE_INPUT);
      fftw_execute(p3); 
      fftw_execute(p4); 
      fftw_destroy_plan(p3);
      fftw_destroy_plan(p4); 
  </code></pre>
  
  <p>Regards</p>
  
  <p>Antonio</p>