Train: Detect and correct edge case when peoplePerBatch > number of classes.

Thanks @venturamartin90

training/main.lua

@@ -28,6 +28,14 @@ paths.dofile('train.lua')
 paths.dofile('test.lua')
 paths.dofile('util.lua')
 
+if opt.peoplePerBatch > #trainLoader.classes then
+  print('\n\nWarning: opt.peoplePerBatch > number of classes.')
+  print('  + opt.peoplePerBatch: ', opt.peoplePerBatch)
+  print('  + number of classes: ', #trainLoader.classes)
+  print('Setting opt.peoplePerBatch to the number of classes.\n\n')
+  opt.peoplePerBatch = #trainLoader.classes
+end
+
 epoch = opt.epochNumber
 
 -- test()

training/train.lua

@@ -167,7 +167,8 @@ function trainBatch(inputsThread, numPerClassThread)
          for k = 1,numImages do
             if k < embStartIdx or k > embStartIdx+n-1 then
                local negDist = dist(embeddings[aIdx], embeddings[k])
-               if posDist < negDist and negDist < selNegDist and negDist < alpha then
+               if posDist < negDist and negDist < selNegDist and
+                    math.abs(posDist - negDist) < alpha then
                   selNegDist = negDist
                   selNegIdx = k
                end