From: Michael Orlitzky <michael@orlitzky.com>
Date: Fri, 22 Mar 2013 19:48:12 +0000 (-0400)
Subject: Fix the iteration count in the PCGM.
X-Git-Url: https://gitweb.michael.orlitzky.com/?a=commitdiff_plain;h=302a62bb7c0adf581916fcd1f93faa719e8d51e8;p=octave.git

Fix the iteration count in the PCGM.
---

diff --git a/optimization/preconditioned_conjugate_gradient_method.m b/optimization/preconditioned_conjugate_gradient_method.m
index 4e68ccb..35fecaa 100644
--- a/optimization/preconditioned_conjugate_gradient_method.m
+++ b/optimization/preconditioned_conjugate_gradient_method.m
@@ -77,7 +77,7 @@ function [x, k] = preconditioned_conjugate_gradient_method(Q, ...
   zk = M \ rk;
   dk = -zk;
 
-  for k = [ 0 : max_iterations ]
+  while (k <= max_iterations)
 
     if (norm(rk) < tolerance)
       % Check our stopping condition. This should catch the k=0 case.
@@ -109,6 +109,10 @@ function [x, k] = preconditioned_conjugate_gradient_method(Q, ...
     beta_next = (r_next' * z_next)/rkzk;
     d_next = -z_next + beta_next*dk;
 
+    % We potentially just performed one more iteration than necessary
+    % in order to simplify the loop. Note that due to the structure of
+    % our loop, we will have k > max_iterations when we fail to
+    % converge.
     k = k + 1;
     xk = x_next;
     rk = r_next;