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The nested for loops discussed above are included in the code shown in Listing 15 . As suggested above, the outer loop iterates on frequency while the inner loop iterates on the values that make up the incoming samples. The code inthe inner loop computes the sum of the product of the time series and the reference cosine and sine functions.
Listing 15. The remainder of the method and the class. |
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//Outer loop iterates on frequency
// values.for(int i=0; i<dataLen;i++){
double freq = lowF + i*delF;double real = 0.0;
double imag = 0.0;double ang = 0.0;
//Inner loop iterates on time-// series points.
for(int j=0; j<dataLen; j++){
real += data[j]*Math.cos(
2*pi*freq*(j-zero));imag += data[j]*Math.sin(2*pi*freq*(j-zero));
}//end inner looprealOut[i]= real/dataLen;
imagOut[i]= imag/dataLen;
magnitude[i]= (Math.sqrt(
real*real + imag*imag))/dataLen;//Calculate and return the phase
// angle in degrees.if(imag == 0.0&&real == 0.0){ang = 0.0;}
else{ang = Math.atan(imag/real)*180.0/pi;}if(real<0.0&&imag == 0.0){ang = 180.0;}
else if(real<0.0&&imag == -0.0){
ang = -180.0;}else if(real<0.0&&imag>0.0){
ang += 180.0;}else if(real<0.0&&imag<0.0){
ang += -180.0;}angleOut[i] = ang;}//end outer loop
}//end transform method}//end class ForwardRealToComplex01 |
At the end of each iteration of the inner loop, code in the outer loop deposits the real, imaginary, magnitude, and phase angle results in the outputarray objects. To accomplish this, the code:
Now you know about the DFT algorithm. You also know about some of the fundamental aspects of spectral analysis involving the sampling frequency andthe folding frequency.
Future modules will discuss other aspects of spectral analysis including:
At this point, I will present a similar spectral analysis program that uses an FFT algorithm. I will present this program with very little discussion. I amproviding it in this module for two primary purposes:
The program named Dsp030 is very similar to Dsp028 . The major differences are:
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