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Corrected a bug leading to infinite loops with flat objectives #1542

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Corrected a bug leading to infinite loops with flat objectives #1542

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10 changes: 6 additions & 4 deletions pylearn2/optimization/batch_gradient_descent.py
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Original file line number Diff line number Diff line change
Expand Up @@ -350,9 +350,10 @@ def minimize(self, * inputs):
if self.verbose:
logger.info('\t{0} {1}'.format(alpha, obj))

# Use <= rather than = so if there are ties
# the bigger step size wins
if obj <= best_obj:
# Should not use <= instead of < because, for a flat
# objective, this leads to an infinite loop due to the
# condition used to grow the step sizes
if obj < best_obj:
best_obj = obj
best_alpha = alpha
best_alpha_ind = ind
Expand All @@ -374,7 +375,8 @@ def minimize(self, * inputs):
alpha_list = [alpha / 3. for alpha in alpha_list]
if self.verbose:
logger.info('shrinking the step size')
elif best_alpha_ind > len(alpha_list) - 2:
elif best_alpha_ind >= len(alpha_list) - 1:
# Grow the step size if the last step size was used
alpha_list = [alpha * 2. for alpha in alpha_list]
if self.verbose:
logger.info('growing the step size')
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