converts a NA to a specified value
v=missrv(mat,val)
* mat = a (nxp) matrix
* val = a scalar
x1=ones(7,1);x1(2)=%nan;x1(5)=%nan;z=missrv(x1,5) //returns: //z = //! 1. ! //! 5. ! //! 1. ! //! 1. ! //! 5. ! //! 1. ! //! 1. !