x=testmatrix('magic',4);/// \sleftarrow{\normalfont a \verb+4x4+ test matrix }
fd=mopen('save.dat','wb'); /// \sleftarrow {\begin{minipage}[t]{5cm}{\nf{}opens a file {for} writing in binary \\ mode (\verb+'b'+ is useful on windows) }\end{minipage}}
mput(length('x'),'i',fd) /// \sleftarrow{\normalfont writes an integer. The length of the string \verb+'x'+}
mputstr('x',fd) ;     /// \sleftarrow{\normalfont writes a string \verb+'x'+}
mput(size(x,'r'),'i',fd) /// \sleftarrow{\normalfont writes an integer (number of rows)}
mput(size(x,'c'),'i',fd) /// \sleftarrow{\normalfont writes an integer (number of columns)}
mput(x,'d',fd);   /// \sleftarrow{\normalfont writes an array of doubles }
mclose(fd);     /// \sleftarrow{\normalfont closes the file output stream}
clear x; 

fd=mopen('save.dat','rb'); /// \sleftarrow{\normalfont opens a file {for} reading in binary mode}
ls=mget(1,'i',fd);          /// \sleftarrow{\normalfont reads an integer }
name=mgetstr(ls,fd); /// \sleftarrow{\normalfont reads a string. The string length is given by \verb+ls+}
m=mget(1,'i',fd);n=mget(1,'i',fd);  /// \sleftarrow{\normalfont reads two integers  \verb+m+ and \verb+n+}
data=mget(m*n,'d',fd);/// \sleftarrow{\normalfont reads \verb+m*n+ doubles in a vector }
code= msprintf('%s=matrix(data,%d,%d);',name,m,n); 
execstr(code);  /// \sleftarrow{\normalfont reshape the matrix and give it   the correct name (i.e \verb+x+)}
mclose(fd) ;     /// \sleftarrow{\normalfont close the file }
and(x == testmatrix('magic',4))  /// \sleftarrow{\normalfont test }