[fixes #20] Implement Inverse Short Time Fourier Transform

src/main/java/com/github/psambit9791/jdsp/filter/FIRWin2.java

@@ -217,7 +217,7 @@ public double[] computeCoefficients(double[] cutoff, double[] gain) {
         // Perform the Inverse DFT
         InverseDiscreteFourier transform = new InverseDiscreteFourier(fx2D, true);
         transform.idft();
-        double[] outFull = transform.getRealSignal();
+        double[] outFull = transform.getReal();
 
         Hamming w = new Hamming(this.numTaps);
         double[] window = w.getWindow();

src/main/java/com/github/psambit9791/jdsp/signal/Resample.java

@@ -170,7 +170,7 @@ private void resample_fft() {
 
         DiscreteFourier df = new DiscreteFourier(this.signal);
         df.dft();
-        double[][] X = df.getFull(true);
+        double[][] X = df.getComplex2D(true);
         double[][] Y = new double[this.num/2+1][2];
 
         int N = Math.min(this.num, Nx);
@@ -195,7 +195,7 @@ private void resample_fft() {
 
         InverseDiscreteFourier idf = new InverseDiscreteFourier(Y, true);
         idf.idft();
-        double[] y = idf.getRealSignal();
+        double[] y = idf.getReal();
         this.output = MathArrays.scale((float)this.num/(float)Nx, y);
     }
 

src/main/java/com/github/psambit9791/jdsp/transform/DiscreteFourier.java

@@ -134,12 +134,12 @@ public double[][] getMagPhaseDeg(boolean onlyPositive) throws ExceptionInInitial
     }
 
     /**
-     * Returns the complex value of the discrete fourier transformed sequence
+     * Returns the complex value of the discrete fourier transformed sequence as a 2D matrix
      * @param onlyPositive Set to True if non-mirrored output is required
      * @throws java.lang.ExceptionInInitializerError if called before executing dft() method
      * @return double[][] The complex DFT output; first array column = real part; second array column = imaginary part
      */
-    public double[][] getFull(boolean onlyPositive) throws ExceptionInInitializerError {
+    public double[][] getComplex2D(boolean onlyPositive) throws ExceptionInInitializerError {
         Complex[] dftout = getComplex(onlyPositive);
         return UtilMethods.complexTo2D(dftout);
     }

src/main/java/com/github/psambit9791/jdsp/transform/Hilbert.java

@@ -65,7 +65,7 @@ private void fillH() {
     public void hilbertTransform() {
         DiscreteFourier dft = new DiscreteFourier(this.signal);
         dft.dft();
-        double[][] dftOut = dft.getFull(false);
+        double[][] dftOut = dft.getComplex2D(false);
 
         double[][] modOut = new double[dftOut.length][dftOut[0].length];
 
@@ -76,7 +76,7 @@ public void hilbertTransform() {
 
         InverseDiscreteFourier idft = new InverseDiscreteFourier(modOut, false);
         idft.idft();
-        this.output = idft.getAsComplex();
+        this.output = idft.getComplex();
     }
 
     /**

src/main/java/com/github/psambit9791/jdsp/transform/InverseDiscreteFourier.java

@@ -12,10 +12,12 @@
 
 import org.apache.commons.math3.complex.Complex;
 
+import java.util.Arrays;
+
 /**
  * <h1>Inverse Discrete Fourier Transform</h1>
  * The InverseDiscreteFourier class applies the inverse discrete fourier transform on the input sequence (real/complex) and
- * provides different representations of the reconstructed signal to be returned (real signal, complex signal, absolute signal)
+ * provides different representations of the reconstructed signal to be returned (real signal, complex signal, ...)
  * <p>
  *
  * @author  Sambit Paul
@@ -76,15 +78,38 @@ public void idft() {
         }
     }
 
+    /**
+     * This method returns the complex value of the generated signal as a Complex array.
+     * @throws java.lang.ExceptionInInitializerError if called before executing idft() method
+     * @return Complex[] The signal (complex)
+     */
+    protected Complex[] getComplex() throws ExceptionInInitializerError {
+        checkOutput();
+        return this.signal;
+    }
+
+    /**
+     * This method returns the complex value of the generated signal as a 2D matrix.
+     * @throws java.lang.ExceptionInInitializerError if called before executing idft() method
+     * @return double[][] The signal (complex)
+     */
+    public double[][] getComplex2D() throws ExceptionInInitializerError {
+        checkOutput();
+        double[][] ret = new double[this.signal.length][2];
+        for (int i=0; i<ret.length; i++) {
+            ret[i][0] = this.signal[i].getReal();
+            ret[i][1] = this.signal[i].getImaginary();
+        }
+        return ret;
+    }
+
     /**
      * This method returns the real part of the generated signal.
      * @throws java.lang.ExceptionInInitializerError if called before executing idft() method
      * @return double[] The signal (real part)
      */
-    public double[] getRealSignal() throws ExceptionInInitializerError {
-        if (this.signal == null) {
-            throw new ExceptionInInitializerError("Execute idft() function before returning result");
-        }
+    public double[] getReal() throws ExceptionInInitializerError {
+        checkOutput();
         double[] ret = new double[this.signal.length];
         for (int i=0; i<ret.length; i++) {
             ret[i] = this.signal[i].getReal();
@@ -93,52 +118,47 @@ public double[] getRealSignal() throws ExceptionInInitializerError {
     }
 
     /**
-     * This method returns the absolute value of the generated signal.
+     * This method returns the imaginary part of the generated signal.
      * @throws java.lang.ExceptionInInitializerError if called before executing idft() method
-     * @return double[] The signal (absolute)
+     * @return double[] The signal (imaginary part)
      */
-    public double[] getAbsoluteSignal() throws ExceptionInInitializerError {
-        if (this.signal == null) {
-            throw new ExceptionInInitializerError("Execute idft() function before returning result");
-        }
+    public double[] getImaginary() throws ExceptionInInitializerError {
+        checkOutput();
         double[] ret = new double[this.signal.length];
         for (int i=0; i<ret.length; i++) {
-            ret[i] = this.signal[i].abs();
+            ret[i] = this.signal[i].getImaginary();
         }
         return ret;
     }
 
     /**
-     * This method returns the complex value of the generated signal as a 2D matrix.
+     * This method returns the magnitude value of the IDFT result.
      * @throws java.lang.ExceptionInInitializerError if called before executing idft() method
-     * @return double[][] The signal (complex)
+     * @return double[] The signal (magnitude)
      */
-    public double[][] getComplexSignal() throws ExceptionInInitializerError {
-        if (this.signal == null) {
-            throw new ExceptionInInitializerError("Execute idft() function before returning result");
-        }
-        double[][] ret = new double[this.signal.length][2];
+    public double[] getMagnitude() throws ExceptionInInitializerError {
+        checkOutput();
+        double[] ret = new double[this.signal.length];
         for (int i=0; i<ret.length; i++) {
-            ret[i][0] = this.signal[i].getReal();
-            ret[i][1] = this.signal[i].getImaginary();
+            ret[i] = this.signal[i].abs();
         }
         return ret;
     }
 
     /**
-     * This method returns the complex value of the generated signal as a Complex array.
+     * This method returns the phase value of the IDFT result.
      * @throws java.lang.ExceptionInInitializerError if called before executing idft() method
-     * @return double[] The signal (complex)
+     * @return double[] phase of the signal
      */
-    protected Complex[] getAsComplex() throws ExceptionInInitializerError
-    {
-        if (this.signal == null) {
-            throw new ExceptionInInitializerError("Execute idft() function before returning result");
+    public double[] getPhase() throws ExceptionInInitializerError {
+        checkOutput();
+        double[] ret = new double[this.signal.length];
+        for (int i=0; i<ret.length; i++) {
+            ret[i] = this.signal[i].getArgument();
         }
-        return this.signal;
+        return ret;
     }
 
-
     private void idftRealFull() {
         Complex[] out = new Complex[this.real_sequence.length];
 
@@ -228,4 +248,10 @@ private void idftComplexMirror() {
         }
         this.signal = out;
     }
+
+    private void checkOutput() {
+        if (this.signal == null) {
+            throw new ExceptionInInitializerError("Execute idft() function before returning result");
+        }
+    }
 }