there are certain situations in which the use of unequal mesh size in different coordinate direction is more cost effective.In those situation,the physical quantity modeled may have uneven distribution in different direction.A typical example is to model the temperature distribution in a thin rod,in which the physical domain in one direction is much longer than that in the other direction.Another example is in microscale heat-transfer modelling problems,in which the thickness of one dimension is at the micriscale, but those of the other dimensions are not