Fix a comment.

[octave.git] / optimization / preconditioned_conjugate_gradient_method.m

diff --git a/optimization/preconditioned_conjugate_gradient_method.m b/optimization/preconditioned_conjugate_gradient_method.m
index cd886084a9766e1d785df59185c358ae69d75cc7..f3ff7e2fd56b36e99d6c478cb1a75a18f2bbe170 100644 (file)
--- a/optimization/preconditioned_conjugate_gradient_method.m
+++ b/optimization/preconditioned_conjugate_gradient_method.m
@@ -14,8 +14,7 @@ function [x, k] = preconditioned_conjugate_gradient_method(Q, ...
   %   min [phi(x) = (1/2)*<Qx,x> + <b,x>]
   %
   % using the preconditioned conjugate gradient method (14.56 in
-  % Guler). If ``M`` is the identity matrix, we use the slightly
-  % faster implementation in conjugate_gradient_method.m.
+  % Guler).
   %
   % INPUT:
   %
@@ -66,7 +65,8 @@ function [x, k] = preconditioned_conjugate_gradient_method(Q, ...
   %
 
   % We use this in the inner loop.
-  sqrt_n = floor(sqrt(length(x0)));
+  n = length(x0);
+  sqrt_n = floor(sqrt(n));
 
   % Set k=0 first, that way the references to xk,rk,zk,dk which
   % immediately follow correspond (semantically) to x0,r0,z0,d0.
@@ -90,8 +90,8 @@ function [x, k] = preconditioned_conjugate_gradient_method(Q, ...
 
     % So if it's too close to zero, we replace it with something
     % comparable but non-zero.
-    if (abs(dkQdk) < eps)
-      dkQdk = sign(dkQdk)*eps;
+    if (dkQdk < eps)
+      dkQdk = eps;
     end
 
     alpha_k = rkzk/dkQdk;