1) DFTI is good for FFTs. Intel MKL also provides FFTW3 interface. What one buys depends on goals. If you are sure the perfromance critical part of your application is FFT then MKL may bejust right choice.Intel C++ Compiler ProfessionalEdition may give additional boost to the algorithms coded in you sources, which may be essential for C++ code.Please refer to Intel Software Development Products page for more information.
2) Yes, 30-day evaluation versions are available
3 and 4) For GUI programming, such as displaying graphical information let me refer you to Qt library.
I would like to follow up with someone please on my inquiry that I had made in my first post.
Let me say that I would like to evaluate FFT done by the function DftiComputeForward(...) from the Intel Math Kernel Library for Windows at $399.
The function would return 0 for success or non-zero for failure.
The FFT in theory returns something else, i.e. a sine wave of frequency f is input and the FFT obtains the Dirac function, andon the x axis of frequency domain the Dirac function is centered at the central frequency f.
A way to evaluate the DftiComputeForward(...) would be to visualize the frequency domain.
A way to display the frequency domain with graphs would be with functions from the QT library:
There are many ways to test DftiComputeForward(), few of them require Qt. Possibly the simplest one is to print the data into a file, and then visuzliseit using your favourite plotting tool, such as Microsoft Excel or gnuplot.
If you want to visualise it in your application, then you should program the visualization yourself, and Qt would be a nice tool for that, because it was designed to write portable Graphical User Interfaces efficiently. Please refer to Qt documentation/forums about how to do this.
Of course there must be other tools around that would help you to build a GUI to monitoryour converter, just google. However, MKL is the right choice to do the FFT.