From b81c9fc23908eff3f92bc5cb9cb1485ca6a9d4b2 Mon Sep 17 00:00:00 2001
From: Aadi B <122440845+aadi-bh@users.noreply.github.com>
Date: Sat, 25 Nov 2023 00:51:36 +0530
Subject: [PATCH] Add `ggb.py`

---
 ggb.py | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 ggb.py

diff --git a/ggb.py b/ggb.py
new file mode 100644
index 0000000..d2ed109
--- /dev/null
+++ b/ggb.py
@@ -0,0 +1,37 @@
+# Gegenbauer polynomials -- the Gibbs complimentary basis to Fourier
+
+import numpy as np
+from scipy.special import gegenbauer as ggb
+from scipy.special import gamma, factorial
+
+'''
+Maps interval [a,b] to [-1,1]
+'''
+def z(y, a, b):
+    return -1 + 2 * (y-a)/(b-a)
+
+'''
+Weight function
+'''
+def w(x, lam):
+    return np.power(1-np.power(x,2), lam-0.5)
+
+'''
+Ggb polynomial of order n evaluated at x
+'''
+def C(x, n, lam):
+    return ggb(n, lam)(x)
+
+'''
+Square of weighted norm of C(n, lam)
+'''
+def gam(n, lam):
+    r = np.sqrt(np.pi)
+    r *= gamma(n + 2*lam) * gamma(lam + 0.5) 
+    r /= gamma(lam) * gamma(2 * lam) * factorial(n) * (n+lam)
+    return r
+
+# TODO
+# Need a way to compute the inner product on an arbitrary interval
+# Expand it in terms of the ggbs
+# Patch it back into the solution.