1. A method of operating a classical computer having display, storage and calculation means, to calculate a q-net data-set based on a c-net data-set with the purpose of inducing a quantum computer to calculate a desired probability that depends on said c-net data-set, said method comprising the steps of: displaying on said display means a c-graph comprising a plurality of N c-nodes, and a plurality of directed c-lines connecting certain pairs of said c-nodes, storing said c-net data-set in said storage means, wherein said c-net data-set comprises: (a) c-graph information comprising a c-node label for each of said N c-nodes, and also comprising, for each said directed c-line, said c-node label for the source c-node and for the destination c-node of the directed c-line, (b) c-state information comprising, for each j∈{1, 2,. .. N}, a finite set S j containing labels for the states that the j'th c-node {circumflex over (x)} j may assume, and (c) c-probability information comprising, for each j∈{1, 2,. .. N}, a representation of a non-negative real number P j [ x j ❘ x k 1 , x k 2 , … ⁢ , x k  Γ j  ] for each vector ( x j , ( x. ) Γ j ) = ( x j , x k 1 , x k 2 , … ⁢ , x k  Γ j  ) such that x j ∈S j , x k 1 ∈S k 1 , x k 2 ∈S k 2 ,. .. , and x k  Γ j  ∈ S k  Γ j  , wherein ( x ^ k 1 , x ^ k 2 , … ⁢ , x ^ k  Γ j  ) are the |Γ j | c-nodes connected to {circumflex over (x)} j by directed c-lines entering {circumflex over (x)} j , wherein said |Γ j | is an integer greater or equal to zero, composing said q-net data-set with said calculation means and using said c-net data-set, wherein said q-net data-set comprises (a′) q-graph information comprising a q-node label for each q-node of a plurality of N′ q-nodes, and also comprising a plurality of directed q-lines, wherein a directed q-line comprises an ordered pair of said q-node labels, wherein one member of the label pair labels the source q-node and the other member labels the destination q-node of the directed q-line, (b′) q-state information comprising, for each j∈{1, 2,. .. N′}, a finite set S′ j containing labels for the states that the j'th q-node ŷ j may assume, and (c′) q-amplitude information comprising, for each j∈{1, 2. .. N′}, a representation of a complex number A j [ y j ❘ y k 1 , y k 2 , … ⁢ , y k  Γ j ′  ] for each vector ( y j , ( y. ) Γ j ′ ) = ( y j , y k 1 , y k 2 , … ⁢ , y k  Γ j ′  ) such that y j ∈S′ j , y k 1 ∈S′ k 1 , y k 2 ∈S′ k 2 ,. .. , and y k  Γ j ′  ∈ S k  Γ j ′  ′ , wherein ( y ^ k 1 , y ^ k 2 , … ⁢ , y ^ k  Γ j ′  ) are the |Γ′ j | nodes connected to ŷ j by directed lines entering ŷ j , wherein said |Γ′ j | is an integer greater or equal to zero, wherein if P ⁡ ( x. ) = ∏ j = 1 N ⁢ P j ⁡ [ x j ❘ ( x. ) Γ j ] / ( ∑ ( x. ) ⁢ numerator ) , and A ⁡ ( y. ) = ∏ j = 1 N ′ ⁢ A j ⁡ [ y j ❘ ( y. ) Γ j ′ ] / ( ∑ ( y. ) ⁢  numerator  2 ) , and L is the set of all j such that ŷ j is a leaf node of said q-net data-set, and not ⁡ ( L ) = { 1 , 2 , … ⁢ ⁢ N ′ } - L , and A L ⁡ [ ( y. ) L ] = ∑ ( y. ) not ⁡ ( L ) ⁢ A ⁡ ( y. ) , then, for all x 1 ∈S 1 , x 2 ∈S 2 ,. .. , and x N ∈S N , P(x.) is a sum of some numbers from the set {|A L [(y.) L ]| 2 : for all possible values of (y.) L }.