Ticket #581: chebwin_patch.diff

scipy/signal/signaltools.py

@@ -855 +855 @@
         M = M+1
 
     # compute the parameter beta
-    beta = cosh(1.0/(M-1.0)*arccosh(10**(at/20.)))
+    beta = cosh(1.0/(M-1.0)*arccosh(10**(abs(at)/20.)))
     k = r_[0:M]*1.0
     x = beta*cos(pi*k/M)
-    #find the window's DFT coefficients
-    p = zeros(x.shape) * 1.0
-    for i in range(len(x)):
-        if x[i] < 1:
-            p[i] = cos((M - 1) * arccos(x[i]))
-        else:
-            p[i] = cosh((M - 1) * arccosh(x[i]))
-
+    # find the window's DFT coefficients
+    # using the Chebyshev polynomial
+    p = polyval(special.chebyt(M - 1), x)
     # Appropriate IDFT and filling up
     # depending on even/odd M
     if M % 2:
-        w = real(fft(p));
+        w = real(fft(p * 1.0));
         n = (M + 1) / 2;
         w = w[:n] / w[0];
-        w = concatenate((w[n - 1:0:-1], w))
+        w = numpy.core.concatenate((w[n - 1:0:-1], w))
     else:
         p = p * exp(1.j*pi / M * r_[0:M])
         w = real(fft(p));
         n = M / 2 + 1;
         w = w / w[1];
-        w = concatenate((w[n - 1:0:-1], w[1:n]));
+        w = numpy.core.concatenate((w[n - 1:0:-1], w[1:n]));
     if not sym and not odd:
         w = w[:-1]
     return w