You can use
detector = trainYOLOv2ObjectDetector(trainingData,checkpoint,options)
to resume training from a specific checkpoint. The checkpoint is specified as a yolov2ObjectDetector object. This means that you would want to save this checkpoint during your initial training of the YOLOv2 model periodically. To do that specify a CheckpointPath before training.
You can then load the checkpoint like this:
data = load('/yourpathtothemodel/checkpath/yolov2_checkpoint__216__2018_11_16__13_34_30.mat');
checkpoint = data.detector;
So the initial training of your model should look similar to this:
detector = trainYOLOv2ObjectDetector(trainingData,lgraph,options)
where options is defined before the execution of the training method and has the CheckpointPath to your local dictionary:
options = trainingOptions('sgdm',...
'InitialLearnRate',0.001,...
'Verbose',true,...
'MiniBatchSize',16,...
'MaxEpochs',30,...
'Shuffle','never',...
'VerboseFrequency',30,...
'CheckpointPath',"C:\yourpathtothemodel);