FFT.FftShift()

resolves #69 and extends  #68

dev/python/fftshift.py

@@ -0,0 +1,12 @@
+import scipy.fft
+import numpy as np
+
+if __name__ == "__main__":
+
+    values = np.arange(7)
+    print(values)
+    print(scipy.fft.fftshift(values))
+
+    values = np.arange(8)
+    print(values)
+    print(scipy.fft.fftshift(values))

src/FftSharp.Tests/FftTests.cs

@@ -46,4 +46,22 @@ public void Test_FFT_FrequencyScale()
             Assert.AreEqual(fftFreq[i], fftFreq[i], 1e-10);
         }
     }
+
+    [Test]
+    public void Test_FftShift_Odd()
+    {
+        double[] values = { 0, 1, 2, 3, 4, 5, 6 };
+        double[] shifted = FFT.FftShift(values);
+        double[] expectedResult = { 4, 5, 6, 0, 1, 2, 3 };
+        Assert.AreEqual(expectedResult, shifted);
+    }
+
+    [Test]
+    public void Test_FftShift_Even()
+    {
+        double[] values = { 0, 1, 2, 3, 4, 5, 6, 7 };
+        double[] shifted = FFT.FftShift(values);
+        double[] expectedResult = { 4, 5, 6, 7, 0, 1, 2, 3 };
+        Assert.AreEqual(expectedResult, shifted);
+    }
 }

src/FftSharp/FFT.cs

@@ -216,4 +216,18 @@ public static double[] Power(System.Numerics.Complex[] spectrum, bool positiveOn
 
         return output;
     }
+
+    /// <summary>
+    /// Return a copy of the given values with the zero frequency component shifted to the center.
+    /// </summary>
+    public static double[] FftShift(double[] values)
+    {
+        int shiftBy = (values.Length + 1) / 2;
+
+        double[] values2 = new double[values.Length];
+        for (int i = 0; i < values.Length; i++)
+            values2[i] = values[(i + shiftBy) % values.Length];
+
+        return values2;
+    }
 }