1. A hard magnetic bubble domain analog multiplier comprising: a strip layer of hard bubble domain magnetic material capable of sustaining a hard bubble domain, said strip layer having an elongated area therein defining a bubble domain propagating channel, said channel having an axis of net displacement of bubble domain motion extending substantially parallel to opposite side boundaries of said propagating channel; means including a bias magnetic field for maintaining at least one hard magnetic bubble domain in said propagating channel; means producing a domain diameter control magnetic field into said strip layer so as to have an instantaneously uniform intensity throughout said domain propagating channel; a first input current signal means responsive to a first quantity to be computed upon for cyclically varying said domain diameter control field in response to cyclic variations of the first quantity; means producing a driving field gradient into said strip layer so as to have a gradient direction of maximum increasing intensity across said domain propagating channel so that the direction of the driving field gradient is substantially perpendicular to the net displacement axis; a second input signal means for cyclically varying said driving field gradient in response to the cyclic variations of a second quantity to be computed upon by being multiplied by said first quantity whereby the combined cyclic variations of said domain diameter control field and said driving field gradient produce orbital domain movements having average movement along the net displacement axis of said domain propagating channel at an average velocity directly proportional to the product of said domain diameter control field and said driving field gradient thereby producing a domain net displacement proportional to the time integral of the product of said first and second quantities.