Imlemented by Abinash Singh During FOSSEE Semester Long Fellowship 2024

1 files changed, 63 insertions, 39 deletions

diff --git a/macros/czt.sci b/macros/czt.sci
index 84a0253..f7c4138 100644
--- a/macros/czt.sci
+++ b/macros/czt.sci
@@ -1,41 +1,65 @@
-function y = czt(x, varargin)
-//Chirp Z Transform
-//Calling Sequence
-//czt (x)
-//czt (x, m)
-//czt (x, m, w)
-//czt (x, m, w, a)
-//Parameters 
-//x: Input scalar or vector
-//m: Total Number of steps
-//w: ratio between points in each step
-//a: point in the complex plane 
-//Description
-//This is an Octave function.
-//Chirp z-transform. Compute the frequency response starting at a and stepping by w for m steps. a is a point in the complex plane, and w is the ratio between points in each step (i.e., radius increases exponentially, and angle increases linearly).
-//Examples
-// m = 32;                               ## number of points desired
-// w = exp(-j*2*pi*(f2-f1)/((m-1)*Fs));  ## freq. step of f2-f1/m
-// a = exp(j*2*pi*f1/Fs);                ## starting at frequency f1
-// y = czt(x, m, w, a);
-
-funcprot(0);
-lhs= argn(1);
-rhs= argn(2);
-
-if(rhs<1 | rhs > 4)
-error("Wrong number of input arguments")
-end
-
-select (rhs)
-	case 1 then
-		y= callOctave("czt", x);
-	case 2 then
-		y= callOctave("czt", x, varargin(1));
-	case 3 then
-		y= callOctave("czt", x, varargin(1), varargin(2));
-	case 4 then
-		y= callOctave("czt", x, varargin(1), varargin(2), varargin(3));
-end
+/*Description
+        Chirp z-transform. Compute the frequency response starting at a and stepping by w for m steps. a is a point in the complex plane,
+        and w is the ratio between points in each step (i.e., radius increases exponentially, and angle increases linearly).
+  Calling Sequence
+        czt (x)
+        czt (x, m)
+        czt (x, m, w)
+        czt (x, m, w, a)
+  Parameters
+        x: Input scalar or vector
+        m: Total Number of steps
+        w: ratio between points in each step
+        a: point in the complex plane
+  Examples: This example uses the czt function to determine the frequency components of a signal, as shown in the following
+    t=linspace(0,50,1000); 
+    f=linspace(0,3,1000);    
+    x_t=sin(t) + cos(t*2*%pi);  
+    x_f=czt(x_t);   
+    plot(f,abs(x_f)); */
+function y = czt(x, m, w, a)
+    funcprot(0);
+    nargin=argn(2);
+    if nargin < 1 || nargin > 4 then
+        error("Please input valid number of arguments");
+    end
+    [row, col] = size(x);
+    if row == 1 then
+        x = x(:); col = 1;
+    end
+    if nargin < 2 || isempty(m) then
+        m = max(size(x(:,1)));
+    end
+    if max(size(m) ) > 1 then
+        error("czt: m must be a single element\n");
+    end
+    if nargin < 3 || isempty(w) then
+        w = exp(-2*%i*%pi/m);
+    end
+    if nargin < 4 || isempty(a) then
+        a = 1;
+    end
+    if max(size(w)) > 1 then
+        error("czt: w must be a single element\n");
+    end
+    if max(size(a)) > 1 then
+        error("czt: a must be a single element\n");
+    end
+    // indexing to make the statements a little more compact
+    n = max(size(x(:,1)));
+    N = [0:n-1]'+n;
+    NM = [-(n-1):(m-1)]'+n;
+    M = [0:m-1]'+n;
+    nfft = 2^nextpow2(n+m-1); // fft pad
+    W2 = w.^(([-(n-1):max(m-1,n-1)]'.^2)/2); // chirp
+    for idx = 1:col
+        fg = fft1(x(:,idx).*(a.^-(N-n)).*W2(N), nfft);
+        fw = fft1(1./W2(NM), nfft);
+        gg = ifft1(fg.*fw, nfft);
+        y(:,idx) = gg(M).*W2(M);
+    end
+    if row == 1, y = y.';
+    end
+    y = clean ( y ) ;
 endfunction