The method of moments algorithm has practical limitations as well; the number of calculations required to model a three-dimensional structure of "N" radiating elements is roughly proportional to the cube of "N". Modeling an antenna with 100 wire segments requires 1003 = 1 million calculations. Increasing the number of elements by a factor of 10 requires 10003 = 1 billion calculations, increasing the computing time by a factor of 1000, assuming the simulation completes at all given memory limitations and such. Consequently, there are other approaches such as geometric optics which are preferred for modeling large structures.