Function matmul

src/opr/impl/blas.cpp:616–620

template <typename T>
T matmul(T a, T b, const opr::BatchedMatrixMul::Param& param = {}) {
    if (!a.node() || !b.node())
        return {};
    return opr::BatchedMatrixMul::make(unsafe(a), unsafe(b), param);
}

SafeSymbolVar matmuls(
        SafeSymbolVar x, SafeSymbolVar y,