Add -gpu option in train.lua

lib/settings.lua

@@ -17,6 +17,7 @@ local cmd = torch.CmdLine()
 cmd:text()
 cmd:text("waifu2x-training")
 cmd:text("Options:")
+cmd:option("-gpu", -1, 'GPU Device ID')
 cmd:option("-seed", 11, 'RNG seed')
 cmd:option("-data_dir", "./data", 'path to data directory')
 cmd:option("-backend", "cunn", '(cunn|cudnn)')

train.lua

@@ -203,6 +203,9 @@ local function train()
       collectgarbage()
    end
 end
+if settings.gpu > 0 then
+   cutorch.setDevice(settings.gpu)
+end
 torch.manualSeed(settings.seed)
 cutorch.manualSeed(settings.seed)
 print(settings)