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- Log -----------------------------------------------------------------
commit 6ab5226ca3e32b443d87934ec138ff0efc8aaecc
Author: Raymond Toy <toy.raymond(a)gmail.com>
Date: Wed Apr 11 20:32:23 2012 -0700
First cut at Bessel Y. Not working yet.
diff --git a/qd-bessel.lisp b/qd-bessel.lisp
index e7ca034..588b5af 100644
--- a/qd-bessel.lisp
+++ b/qd-bessel.lisp
@@ -376,6 +376,7 @@
(format t " term = ~S~%" term)
(format t " sum = ~S~%" sum))))))
+;;
;; TODO:
;; o For |z| <= 1 use the series.
;; o Currently accuracy is not good for large z and half-integer
@@ -402,6 +403,41 @@
(+ (/ -1 z)
(sum-ab big-n v z)
(sum-big-ia big-n v z)))))))))
+
+;; Bessel Y
+;;
+;; bessel_y(v, z) = 1/(2*%pi*%i)*(exp(-%i*v*%pi/2)*I(%i*v,z) - exp(%i*v*%pi/2)*I(-%i*z, v))
+;; + z/v/%pi*((1-cos(v*%pi)/z) + S(N,z,v)*cos(v*%pi)-S(N,z,-v))
+;;
+;; where
+;;
+;; S(N,z,v) = sum(alpha[n](z)*a[n](0,v) + beta[n](z)*sum(exp(-k*z)*a[n](k,v),k,1,N),n,0,inf)
+;; + sum(A[n](v)*I[n](N+1/2,z,v),n,0,inf)
+;;
+(defun bessel-y (v z)
+ (flet ((ipart (v z)
+ (let* ((iz (* #c(0 1) z))
+ (c+ (exp (* v (float-pi z) 1/2)))
+ (c- (exp (* v (float-pi z) -1/2)))
+ (i+ (exp-arc-i-2 iz v))
+ (i- (exp-arc-i-2 (- iz) v)))
+ (/ (- (* c- i+) (* c+ i-))
+ (* #c(0 2) (float-pi z)))))
+ (s (big-n z v)
+ (+ (sum-ab big-n v z)
+ (sum-big-ia big-n v z))))
+ (let* ((big-n 100)
+ (vpi (* v (float-pi z)))
+ (c (cos vpi)))
+ (+ (ipart v z)
+ (* (/ z vpi)
+ (+ (/ (- 1 c)
+ z)
+ (* c
+ (s big-n z v))
+ (- (s big-n z (- v)))))))))
+
+
(defun paris-series (v z n)
(labels ((pochhammer (a k)
commit d795ba718dc53f591c82994811f50250aceec1d7
Author: Raymond Toy <toy.raymond(a)gmail.com>
Date: Wed Apr 11 20:15:47 2012 -0700
Add TODO list for bessel-j.
diff --git a/qd-bessel.lisp b/qd-bessel.lisp
index 3958ff2..e7ca034 100644
--- a/qd-bessel.lisp
+++ b/qd-bessel.lisp
@@ -375,13 +375,25 @@
(format t " f = ~S~%" f)
(format t " term = ~S~%" term)
(format t " sum = ~S~%" sum))))))
-
+
+;; TODO:
+;; o For |z| <= 1 use the series.
+;; o Currently accuracy is not good for large z and half-integer
+;; order.
+;; o For real v and z, return a real number instead of complex.
+;; o Handle the case of Re(z) < 0. (The formulas are for Re(z) > 0:
+;; bessel_j(v,z*exp(m*%pi*%i)) = exp(m*v*%pi*%i)*bessel_j(v, z)
+;; o The paper suggests using
+;; bessel_i(v,z) = exp(-v*%pi*%i/2)*bessel_j(v, %i*z)
+;; when Im(z) >> Re(z)
+;;
(defun bessel-j (v z)
(let ((vv (ftruncate v)))
(cond ((= vv v)
;; v is an integer
(integer-bessel-j-exp-arc v z))
(t
+ ;; Need to fine-tune the value of big-n.
(let ((big-n 100)
(vpi (* v (float-pi (realpart z)))))
(+ (integer-bessel-j-exp-arc v z)
commit c0e12ddf6b61f571555d46c6f168e6bebabc80b1
Author: Raymond Toy <toy.raymond(a)gmail.com>
Date: Wed Apr 11 20:06:38 2012 -0700
Correct the computation of alpha and beta.
diff --git a/qd-bessel.lisp b/qd-bessel.lisp
index 0197e7f..3958ff2 100644
--- a/qd-bessel.lisp
+++ b/qd-bessel.lisp
@@ -213,13 +213,13 @@
(defun alpha (n z)
(let ((n (float n (realpart z))))
- (/ (cf-incomplete-gamma (1+ n) (/ z 2))
+ (/ (incomplete-gamma (1+ n) (/ z 2))
(expt z (1+ n)))))
(defun beta (n z)
(let ((n (float n (realpart z))))
- (/ (- (cf-incomplete-gamma (1+ n) (/ z 2))
- (cf-incomplete-gamma (1+ n) (/ z -2)))
+ (/ (- (incomplete-gamma (1+ n) (/ z 2))
+ (incomplete-gamma (1+ n) (/ z -2)))
(expt z (1+ n)))))
;; a[0](k,v) := (k+sqrt(k^2+1))^(-v);
-----------------------------------------------------------------------
Summary of changes:
qd-bessel.lisp | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
1 files changed, 52 insertions(+), 4 deletions(-)
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OCT: A portable Lisp implementation for quad-double precision floats