运行如下程序：

xi: reg new_pro  tri i.ind*i.cou  i.year if for_sha==0, robust

其中ind为产业（60个），cou为国家变量（40个），系统老是显示：

matsize too small

    You have attempted to create a matrix with too many rows or columns or attempted to fit a model with too many variables.  You need to increase matsize; it is

    currently 2000.  Use set matsize; see help matsize.

    If you are using factor variables and included an interaction that has lots of missing cells, either increase matsize or set emptycells drop to reduce the

    required matrix size; see help set emptycells.

    If you are using factor variables, you might have accidentally treated a continuous variable as a categorical, resulting in lots of categories.  Use the c.

    operator on such variables.

输入命令

set matsize 4000

后，运行一段时间，系统显示：op. sys. refuses to provide memory

问题出在哪里？