举例，xi: sgmediation Y, mv(M) iv(X) cv($CV  i.year i.ind  ) quietly
这个中介效应检验很快，
但是加上个体效应i.code 3000多家公司吧
xi: sgmediation Y, mv(M) iv(X) cv($CV  i.year i.ind  i.code ) quietly
然后stata就一直运行，但是一直不动，很久后提示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
    400.  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.
r(908);


设置了set matsize 11000，最大了吧，再运行，还是不动……