handle multi-output operators

src/optimizer/Optimizer.cpp

@@ -20,7 +20,9 @@ void Aidge::Optimizer::resetGrad(std::shared_ptr<GraphView> graphView)
         auto op = node->getOperator();
         if (op->isAtomic()) {
             auto tensorOp = std::static_pointer_cast<OperatorTensor>(op);
-            tensorOp->getOutput(0)->grad()->zeros();
+            for (auto outputTensor : tensorOp->getOutputs()) {
+                outputTensor->grad()->zeros();
+            }
         } else {
             auto metaOp = std::static_pointer_cast<MetaOperator_Op>(op);
             resetGrad(metaOp->getMicroGraph());