how to use parallel computing with train faster rcnn detector.

Hi, I'm trying to use matlab to train my own data set using train faster rcnn function, but when I tried to enable the parallel computing by applying it in the options : optionsStage1 = trainingOptions('sgdm', ... 'MaxEpochs', 10, ... 'InitialLearnRate', 1e-5, ... 'ExecutionEnvironment','parallel',... 'CheckpointPath', 'D:\hope\checkpoint');

% Options for step 2. optionsStage2 = trainingOptions('sgdm', ... 'MaxEpochs', 10, ... 'ExecutionEnvironment','parallel',... 'InitialLearnRate', 1e-5, ... 'CheckpointPath', 'D:\hope\checkpoint');

% Options for step 3. optionsStage3 = trainingOptions('sgdm', ... 'MaxEpochs', 10, ... 'InitialLearnRate', 1e-6, ... 'ExecutionEnvironment','parallel',... 'CheckpointPath', 'D:\hope\checkpoint');

% Options for step 4. optionsStage4 = trainingOptions('sgdm', ... 'MaxEpochs', 10, ... 'InitialLearnRate', 1e-6, ... 'ExecutionEnvironment','parallel',... 'CheckpointPath', 'D:\hope\checkpoint');

options = [ optionsStage1 optionsStage2 optionsStage3 optionsStage4 ];

I'm getting this error message: Error using vision.internal.cnn.parseInputsFasterRCNN>iCheckExecutionEnvironment (line 433) The value of 'options.ExecutionEnvironment' must be 'auto', 'cpu', or 'gpu'. 'multi-gpu' and 'parallel' are not supported.

could you please help me in this part as soon as possible.