I have a function of type
Where $t$ is in hours
The function represents the evolution in a window of 24 hours of a drug blood concentration, after a dose of a drug is given at $t = 0$ to a patient. I would like to use Fourier transform, to identify th best sampling step to reconstruct the concentration curve. Because it is a human whose blood we are sampling here I would like to reduce the sampling as much as possible, with a reconstruction error of around 20%.
I am using Matlab FFT function to compute the function's Fourier transform and plot the spectrum.
However I am not sure if my frequency are in Hertz or Millihertz. Because I am sampling in hours, I am expecting lower frequencies (millihertz), but I am not sure of the logic.
Here is my Matlab Code
clear all; clc;close all; %% Time-domain signal Ts=0.25; % time discretization step t=0:Ts:24 % in hours C=0.31* (exp(-0.267*(t))-exp(-1.72*(t))); figure,plot(t,C); title('Time domain signal'); xlabel('Time in hours ') %Frequency domain signal Via Matlab FFT function F2=fft(C); L=length(F2); figure,plot((0:L-1)*(1/(L*Ts)),abs(F2)); title('Frequency domain signal via FFT of C(t)'); xlabel('Frequency in Hz or Millihertz?')