Changeset 14669

Timestamp:

Mar 7, 2011, 1:39:28 PM (14 years ago)

Author:

R. Matthew Emerson

Message:

In ATAN of a complex argument, compute the value in terms of the
formula for ATANH, that is, use the formula:

atan(z) = atanh(iz)/i = -i atanh(iz).

Fixes ticket:828, and with any luck, won't screw up anything else.

File:

• trunk/source/level-0/l0-float.lisp (modified) (1 diff)

trunk/source/level-0/l0-float.lisp

@@ -746 +746 @@
       (%sf-atan2 (%short-float y) (%short-float x)))
     (if (typep y 'complex)
-      (let* ((iy (* (sqrt -1) y)))
-             (/ (- (log (+ 1 iy)) (log (- 1 iy)))
-                #c(0 2)))
+      ;; atan y = atanh(i*y)/i = -i atanh(i*y)
+      (let* ((iy (complex (- (imagpart y)) (realpart y)))
+             (h (/ (- (log (+ 1 iy)) (log (- 1 iy))) 2))) ;(atanh iy)
+        (complex (imagpart h) (- (realpart h))))
       (if (typep y 'double-float)
         (%double-float-atan! y (%make-dfloat))