First a small clarification; IFFT stands for Inverse-FFT that is a conversion that converts a complex frequency domain spectrum back to a time domain signal. When you write that the output is "summation of N orthogonal sinusoids" it sounds like it is a time domain signal, that is the result of an IFFT operation. However you also write that he output "represent complex weight for corresponding sinusoidal basis function" which sounds more like a frequency domain representation that is the result of an FFT. Can you explain in more details what you try to achieve?
A spectral component represented by a complex number (a+ib) can be converted to the two fundamental values needed to represent a sinusoidal (sine) signal in the time domain. These are the amplitude of the sine tone (r) and its start phase (Theta). The conversion to/from "Complex" from/to "Polar" can be done in LabVIEW using the two primitives "Polar to Complex" and "Complex to Polar". These are located in the Numeric>>Complex palette. The ouptut of an FFT is originally a complex array, but it is usual to convert the result into two real arrays, one representing the "Magnitude" (r) and one representing the "Phase" (Theta or Phi). Then you can graph the Magnitude and the Phase results on two different graphs.
