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- Log ----------------------------------------------------------------- commit 1421224af506145ab18f9f4b412f300c97c11751 Author: Raymond Toy toy.raymond@gmail.com Date: Sun Mar 6 22:38:09 2011 -0500

Document algorithms better.

diff --git a/qd-elliptic.lisp b/qd-elliptic.lisp index 9c56fcd..c29d9ce 100644 --- a/qd-elliptic.lisp +++ b/qd-elliptic.lisp @@ -34,6 +34,12 @@ ;; (1-sqrt(m))/(1+sqrt(m)), and then square this to get mu1. ;; If not, we may choose the wrong branch when computing ;; sqrt(mu1). + ;; + ;; mu = 4*sqrt(m)/(1+sqrt(m))^2 + ;; sqrt(mu1) = (1-sqrt(m))/(1+sqrt(m)) + ;; v = u/(1+sqrt(mu1)) + ;; + ;; Return v, mu, sqrt(mu1) (let* ((root-m (sqrt m)) (mu (/ (* 4 root-m) (expt (1+ root-m) 2))) @@ -42,10 +48,19 @@ (values v mu root-mu1)))

(defun descending-transform (u m) + ;; A&S 16.12.1 + ;; ;; Note: Don't calculate mu first, as given in 16.12.1. We ;; should calculate sqrt(mu) = (1-sqrt(m1)/(1+sqrt(m1)), and ;; then compute mu = sqrt(mu)^2. If we calculate mu first, ;; sqrt(mu) loses information when m or m1 is complex. + ;; + ;; sqrt(mu) = (1-sqrt(m1))/(1+sqrt(m1)) + ;; v = u/(1+sqrt(mu)) + ;; + ;; where m1 = 1-m + ;; + ;; Return v, mu, sqrt(mu) (let* ((root-m1 (sqrt (- 1 m))) (root-mu (/ (- 1 root-m1) (+ 1 root-m1))) (mu (* root-mu root-mu)) @@ -108,6 +123,9 @@ ;; A&S 16.6.1 (sin u)) (t + ;; A&S 16.12.2 + ;; + ;; sn(u|m) = (1 + sqrt(mu))*sn(v|u)/(1 + sqrt(mu)*sn(v|mu)^2) (multiple-value-bind (v mu root-mu) (descending-transform u m) (let* ((new-sn (elliptic-sn-descending v mu))) @@ -172,6 +190,8 @@

(defun jacobi-cn (u m) ;; Use the ascending Landen transformation, A&S 16.14.3. + ;; + ;; cn(u,m) = (1+sqrt(mu1))/mu * (dn(v,mu)^2-sqrt(mu1))/dn(v,mu) (multiple-value-bind (v mu root-mu1) (ascending-transform u m) (let ((d (dn v mu)))

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Summary of changes: qd-elliptic.lisp | 20 ++++++++++++++++++++ 1 files changed, 20 insertions(+), 0 deletions(-)

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