SUBROUTINE covsrt(covar,maska)
        USE nrtype; USE util_minim, ONLY : assert_eq,swap_rv
        IMPLICIT NONE
        REAL(DP), DIMENSION(:,:), INTENT(INOUT) :: covar
        LOGICAL(LGT), DIMENSION(:), INTENT(IN) :: maska
        INTEGER(I4B) :: ma,mfit,j,k
        ma=assert_eq(size(covar,1),size(covar,2),size(maska),'covsrt')
        mfit=count(maska)
        covar(mfit+1:ma,1:ma)=0.0
        covar(1:ma,mfit+1:ma)=0.0
        k=mfit
        do j=ma,1,-1
                if (maska(j)) then
                        call swap_rv(covar(1:ma,k),covar(1:ma,j))
                        call swap_rv(covar(k,1:ma),covar(j,1:ma))
                        k=k-1
                end if
        end do
        END SUBROUTINE covsrt