A function generator. An electron tube is provided having a cathode, and an anode coextensive with and spaced from the cathode so as to form a gap therebetween. The anode is at a higher potential than the cathode so as to create an electric field between the anode and the cathode. A means for obtaining an output from the function generator as a desired function of the input to the function generator is also provided. This means includes a means for providing a magnetic field in the gap which is normal to the electric field and further includes means for varying the direction of the magnetic field. The variation in the electric field is obtained by varying the width of the gap in the direction of the longitudinal axis of the tube. The variation in the magnetic field is obtained by varying the intensity of the magnetic field in the direction of the longitudinal axis of the tube. By use of additional magnetic fields or by separating the cathode and anode into distinct portions, or a combination thereof multiple functions may be provided.