Matmul rework

[ADD] support for Multi-dimensional Matrix Multiplication, following numpy MatMul operation specificities.

In the context of Multi-dimensional MatMul, we consider an N-Dim Tensor as a stack of 2-D matrices having as shape the last two dimensions of the Tensor.

From Numpy documentation:

The behavior depends on the arguments in the following way.

• If both arguments are 2-D they are multiplied like conventional matrices.
• If either argument is N-D, N > 2, it is treated as a stack of matrices residing in the last two indexes and broadcast accordingly.
• If the first argument is 1-D, it is promoted to a matrix by prepending a 1 to its dimensions. After matrix multiplication the prepended 1 is removed.
• If the second argument is 1-D, it is promoted to a matrix by appending a 1 to its dimensions. After matrix multiplication the appended 1 is removed.

src/operator/MatMul.cpp

@@ -20,6 +20,9 @@
 const std::string Aidge::MatMul_Op::Type = "MatMul";
 
 void Aidge::MatMul_Op::computeOutputDims() {
+    if (!getInput(0) || !getInput(1)) {
+        AIDGE_THROW_OR_ABORT(std::runtime_error, "Missing input. Cannot compute output dimensions for MatMul Operator.");
+    }
     if (!getInput(0)->empty() && !getInput(1)->empty())
     {
         const auto dims0 = getInput(0)->dims();
@@ -27,18 +30,14 @@ void Aidge::MatMul_Op::computeOutputDims() {
 
         if (dims0.size() > 2 && dims1.size() > 2)
         {
-            bool supportedSizes = true;
             std::size_t d0 = dims0.size()-3, d1 = dims1.size()-3;
-            while(d0>0 && d1>0 && supportedSizes)
+            for (std::size_t d0 = dims0.size()-3, d1 = dims1.size()-3; 
+                 (d0>0) && (d1>0);
+                 --d0, --d1)
             {
                 if(dims0[d0] != dims1[d1])
-                    supportedSizes = false;
-
-                d0--;
-                d1--;
+                    AIDGE_THROW_OR_ABORT(std::runtime_error, "Unsupported sizes for MatMul!");
             }
-            if(!supportedSizes)
-                AIDGE_THROW_OR_ABORT(std::runtime_error, "Unsupported sizes for MatMul!");
         }
 
         std::size_t secondToLastIdx2 = dims1.size()>1 ? dims1.size() - 2 : dims1.size() - 1;