NetTrain
NetTrain[net,{input_{1}output_{1},input_{2}output_{2},…}]
trains the specified neural net by giving the input_{i} as input and minimizing the discrepancy between the output_{i} and the actual output of the net, using an automatically chosen loss function.
NetTrain[net,port_{1}{data_{11},data_{12},…},port_{2}{…},…]
trains the specified net by supplying training data at the specified ports.
NetTrain[net,"dataset"]
trains on a named dataset from the Wolfram Data Repository.
NetTrain[net,f]
calls the function f during training to produce batches of training data.
NetTrain[net,data,"prop"]
gives data associated with a specific property prop of the training session.
gives a NetTrainResultsObject[…] that summarizes information about the training session.
Details and Options
 Any input ports of the net whose shapes are not fixed will be inferred from the form of training data, and NetEncoder objects will be attached if the training data contains Image objects, etc.
 Individual training data inputs can be scalars, vectors, numeric tensors. If the net has appropriate NetEncoder objects attached, the inputs can include Image objects, strings, etc.
 Named datasets that are commonly used as examples for neural net applications include the following:

"MNIST" 60,000 classified handwritten digits "FashionMNIST" 60,000 classified images of items of clothing "CIFAR10","CIFAR100" 50,000 classified images of realworld objects "MovieReview" 10,662 movie review snippets with sentiment  Training on a named dataset is equivalent to training on ResourceData["dataset","TrainingSet"]. If a named dataset is used for the ValidationSet option, it is equivalent to ResourceData["dataset","TestSet"].
 Additional forms for specifying training data include {input_{1},input_{2},…}>{output_{1},…} and {port_{1}…,port_{2}…,…,port_{1}…,…,…}.
 When loss layers are automatically attached by NetTrain to output ports, their "Target" ports will be taken from the training data using the same name as the original output port.
 When giving training data using the specification inputs>outputs, the network should not already contain any loss layers and should have precisely one input and one output port.
 The following options are supported:

BatchSize Automatic how many examples to process in a batch LearningRate Automatic rate at which to adjust weights to minimize loss LearningRateMultipliers Automatic set relative learning rates within the net LossFunction Automatic the loss function for assessing outputs MaxTrainingRounds Automatic how many times to traverse the training data Method Automatic the training method to use PerformanceGoal Automatic favor settings with specific advantages TargetDevice "CPU" the target device on which to perform training TimeGoal Automatic number of seconds to train for TrainingProgressMeasurements Automatic measurements to monitor, track and plot during training TrainingProgressCheckpointing None how to periodically save partially trained nets RandomSeeding Inherited how to seed pseudorandom generators internally TrainingProgressFunction None function to call periodically during training TrainingProgressReporting Automatic how to report progress during training TrainingStoppingCriterion None how to automatically stop training ValidationSet None the set of data on which to evaluate the model during training WorkingPrecision Automatic precision of floating point calculations  If the loss is not given explicitly using LossFunction, a loss function will be chosen automatically based on the final layer or layers in the net.
 With the default setting of MaxTrainingRounds>Automatic, training will occur for approximately 20 seconds, but never for more than 10,000 rounds.
 With the setting of MaxTrainingRounds>n, training will occur for n rounds, where a round is defined to be a traversal of the entire training dataset.
 The following settings for ValidationSet can be given:

None use only the existing training set to estimate loss (default) data validation set in the same form as training data Scaled[frac] reserve a specified fraction of the training set for validation {spec,"Interval"int} specify the interval at which to calculate validation loss  For ValidationSet>{spec,"Interval">int}, the interval can be an integer n, indicating that validation loss should be calculated every n training rounds, or a Quantity in units of seconds, minutes or hours.
 For a named dataset such as "MNIST", specifying ValidationSet>Automatic will use the corresponding "TestData" content element.
 If a validation set is specified, NetTrain will return the net that produced the lowest validation loss during training with respect to this set.
 In NetTrain[net,f], the function f is applied to <"BatchSize"n,"Round"r > to generate each batch of training data in the form {input_{1}>output_{1},…} or <"port_{1}">data,… >.
 NetTrain[net,{f,"RoundLength">n}] can be used to specify that f should be applied enough times during a training round to produce approximately n examples. The default is to apply f once per training round.
 NetTrain[net,…,ValidationSet>{g,"RoundLength">n}] can be used to specify that the function g should be applied in an equivalent manner to NetTrain[net,{f,"RoundLength">n}] in order to produce approximately n examples for the purposes of computing validation loss and accuracy.
 Possible settings for WorkingPrecision include:

"Real32" use singleprecision real (32bit) "Real64" use doubleprecision real (64bit) "Mixed" use halfprecision real for certain operations  WorkingPrecision>"Mixed" is only supported for TargetDevice>"GPU", where it can result in significant performance increases on certain devices.
 In NetTrain[net,data,prop], the property prop can be any of the following:

"TrainedNet" the optimal trained network found (default) "BatchesPerRound" the number of batches contained in a single round "BatchLossList" a list of the mean losses for each batch update "BatchMeasurementsLists" list of training measurements associations for each batch update "BatchPermutation" an array of the indices from the training data used to populate each batch "BatchSize" the effective value of BatchSize "BestValidationRound" the training round corresponding to the final trained net "CheckpointingFiles" list of checkpointing files generated during training "ExampleLosses" losses taken by each example during training "ExamplesProcessed" total number of examples processed during training "FinalLearningRate" the learning rate at the end of training "FinalNet" the final network generated in the training process "FinalPlots" association of plots for all losses and measurements "InitialLearningRate" the learning rate at the start of training "LossPlot" a plot of the evolution of the mean training loss "MeanBatchesPerSecond" the mean number of batches processed per second "MeanExamplesPerSecond" the mean number of input examples processed per second "NetTrainInputForm" an expression representing the originating call to NetTrain "OptimizationMethod" the name of the optimization method used "Properties" the full list of available properties "ReasonTrainingStopped" brief description of why training stopped "ResultsObject" a NetTrainResultsObject[…] containing a majority of the available properties in this table "RoundLoss" the mean loss for the most recent round "RoundLossList" a list of the mean losses for each round "RoundMeasurements" association of training measurements for the most recent round "RoundMeasurementsLists" list of training measurements associations for each round "RoundPositions" the batch numbers corresponding to each round measurement "TargetDevice" the device used for training "TotalBatches" the total number of batches encountered during training "TotalRounds" the total number of rounds of training performed "TotalTrainingTime" the total time spent training, in seconds "TrainingExamples" the number of examples in the training set "TrainingNet" the network as prepared for training "ValidationExamples" the number of examples in the validation set "ValidationLoss" the mean loss obtained on the ValidationSet for the most recent validation measurement "ValidationLossList" list of the mean losses on the ValidationSet for each validation measurement "ValidationMeasurements" association of training measurements on the ValidationSet after the most recent validation measurement "ValidationMeasurementsLists" list of training measurements associations on the ValidationSet for each validation measurement "ValidationPositions" the batch numbers corresponding to each validation measurement "WeightsLearningRateMultipliers" an association of the learning rate multiplier used for each weight  An association of the form <"Property">prop,"Form">form,"Interval">int > can be used to specify a custom property whose value will be collected repeatedly during training.
 For a custom property, valid settings for prop can be any of the properties available in TrainingProgressFunction, or a userdefined function that is given the association of all the properties. Valid settings for form include "List", "TransposedList" and "Plot". Valid settings for "Interval" can be "Batch", "Round" or a Quantity[…]. Supported units include "Batches", "Rounds", "Percent" and time units like "Seconds", "Minutes" and "Hours".
 NetTrain[net,data,{prop_{1},prop_{2},…}] returns a list of the results for the prop_{i}.
 NetTrain[net,data,All] returns a NetTrainResultsObject[…] that contains values for all properties that do not require significant additional computation or memory.
 With the default setting of ValidationSet>None, the "TrainedNet" property yields the net as it is at the end of training. When a validation set is provided, the default criterion for selecting the optimal net depends on the type of net:

classification net choose the net with the lowest error rate; ties are broken using the lowest loss nonclassification net choose the net with the lowest loss  The criterion used to select the "TrainedNet" property can be customized using the TrainingStoppingCriterion option.
 The property "BestValidationRound" gives the exact round from which the final net was selected.
 Possible settings for Method include:

"ADAM" stochastic gradient descent using an adaptive learning rate that is invariant to diagonal rescaling of the gradients "RMSProp" stochastic gradient descent using an adaptive learning rate derived from exponentially smoothed average of gradient magnitude "SGD" ordinary stochastic gradient descent with momentum "SignSGD" stochastic gradient descent for which the maginitude of the gradient is discarded  Valid settings for PerformanceGoal include Automatic, "TrainingMemory", "TrainingSpeed" or a list of goals to combine.
 Valid settings for WorkingPrecision include the default value of "Real32", indicating singleprecision floating point; "Real64", indicating doubleprecision floating point; and "Mixed", indicating a mixture of "Real32" and halfprecision. Mixedprecision training is only supported for GPUs.
 Suboptions for specific methods can be specified using Method{"method",opt_{1}val_{1},…}. The following suboptions are supported for all methods:

"LearningRate" Automatic the size of steps to take in the direction of the derivative "LearningRateSchedule" Automatic how to scale the learning rate as training progresses "L2Regularization" None the global loss associated with the L2 norm of all learned arrays "GradientClipping" None the magnitude above which gradients should be clipped "WeightClipping" None the magnitude above which weights should be clipped  With "LearningRateSchedule">f, the learning rate for a given batch will be calculated as initial*f[batch,total], where batch is the current batch number, total is the total number of batches that will be visited during training, and initial is the initial learning rate specified using "LearningRate". The value returned by f should be a number between 0 and 1.
 The suboptions "L2Regularization", "GradientClipping" and "WeightClipping" can be given in the following forms:

r use the value r for all weights in the net {lspec_{1}r_{1},lspec_{2}r_{2},…} use the value r_{i} for the specific part lspec_{i} of the net  The rules lspec_{i}r_{i} are given in the same form as for LearningRateMultipliers.
 For the method "SGD", the following additional suboptions are supported:

"Momentum" 0.93 how much to preserve the previous step when updating the derivative  For the method "ADAM", the following additional suboptions are supported:

"Beta1" 0.9 exponential decay rate for the first moment estimate "Beta2" 0.999 exponential decay rate for the second moment estimate "Epsilon" 0.00001` stability parameter  For the method "RMSProp", the following additional suboptions are supported:

"Beta" 0.95 exponential decay rate for the moving average of the gradient magnitude "Epsilon" 0.000001 stability parameter "Momentum" 0.9 momentum term  For the method "SignSGD", the following additional suboption is supported:

"Momentum" 0.93 how much to preserve the previous step when updating the derivative  If a net already contains initialized or previously trained weights, these will be not be reinitialized by NetTrain before training is performed.
Examples
open all close allBasic Examples (6)
Train a singlelayer linear net on input output pairs:
Predict the value of a new input:
Make several predictions at once:
The prediction is a linear function of the input:
Train a perceptron that classifies inputs as either True or False:
Predict whether a new input is True or False:
Obtain the probability of the input being True by disabling the NetDecoder:
Make several predictions at once:
Plot the probability as a function of the input:
Train a threelayer network to learn a 2D function:
Evaluate the network on an input:
Plot the prediction of the net as a function of x and y:
Train a recurrent network that predicts the maximum value seen in the input sequence:
Evaluate the network on an input:
Plot the output of the network as one element of a sequence is varied:
Train a net and produce a results object that summarizes the training process:
Obtain the trained net from the result:
Obtain the network used to train the net:
Train a net to classify handwritten digits using a named dataset and model: