Abstract
We show that under the matrix product state formalism the states produced in Shor's algorithm can be represented using O(max(, )) space, where l is the number of bits in the number to factorise, and r is the order and the solution to the related order-finding problem. The reduction in space compared to an amplitude formalism approach is significant, allowing simulations as large as 42 qubits to be run on a single processor with 32GB RAM. This approach is readily adapted to a distributed memory environment, and we have simulated a 45 qubit case using 8 cores with 16GB RAM in approximately one hour.