How to solve Exception: No gradient attached to this NDArray

[kameronren]

djl version: 0.11.0
first i write a function: sgd(net.getParameters(), (float)0.2, batchSize); but when I call it, jump out a Exception(No gradient attached to this NDArray, please call array.requiredGradient()on your NDArray or block.setInitializer() on your Block);

so, second I writed a other function:
public static void requiresGrad(ParameterList params) { for (int i = 0; i < params.size(); i++) { NDArray param = params.get(i).getValue().getArray(); param.setRequiresGradient(true); } }. but when I call it( requiresGrad(net.getParameters()); ), jump out a other Exception(The array has not been initialized).

so,third I change the function(requiresGrad) :

public static void requiresGrad(ParameterList params) { for (int i = 0; i < params.size(); i++) { params.get(i).getValue().setInitializer(new NormalInitializer()); params.get(i).getValue().initialize(manager, DataType.FLOAT32); NDArray param = params.get(i).getValue().getArray(); System.out.println(params.get(i).getValue().isInitialized()); param.setRequiresGradient(true); } }. but when I call it ( requiresGrad(net.getParameters()); ),jump out a third Exception( java.lang.NullPointerException: No parameter shape has been set)

how to solve the question? thanks!

[frankfliu]

Please take a look D2L book: https://d2l.djl.ai/chapter_preliminaries/autograd.html

You can get latest version here: https://github.com/deepjavalibrary/d2l-java/blob/master/chapter_preliminaries/autograd.ipynb

[kameronren]

I kown why requiresGrad function is not work! The key point is to put zhe function after the NDList results = net.forward(parameterStore, X, true); If put the requiresGrad function before NDList results = net.forward(parameterStore, X, true); .then we get the Exception(The array has not been initialized)