gaosi.rar_method gauss pivot

program main!主程序 implicit none integer,parameter::n=4 integer i real:: a(n,n),b(n),x(n),js(n) data a / 2.4,-4.0,0.5,0.6,-1.7,2.3,-1.0,8.0,9.0,-1.9,2.0,-1.6,0.9,0.70,1.40,2.50 / b=(/1.5,0.0,5.0,9.0/) call Guass(a,b,n,x,js) write(*,*) 'written by chenke' do i=1,4 write(*,"(1X,'x(',I1,')=',F10.5)") i, x(i) enddo end subroutine Guass(a,b,n,x,js) implicit none integer n,k,i,j,is real:: a(n,n),b(n),x(n),js(n) real :: T,D loop:do k=1,n-1 !全选主元法，从右下角n-k+1阶子阵中选取绝对值最大的元素 D=0.0 do i=k,n do j=k,n if (abs(a(i,j)) > D) then D=abs(a(i,j)) js(k)=j ! 记下最大数值的列数 is=i ! 记下最大数值的行数 endif enddo enddo if (D == 0.0) then write(*,*) 'fail' stop else !对行做出调整 if (is /= k) then do j=k,n T=a(k,j) a(k,j)=a(is,j) a(is,j)=T enddo !对b数组做出对应的调整 T=b(k) b(k)=b(is) b(is)=T endif !对行进行变换 if (js(k) /= k) then do i=1,n T=a(i,k) a(i,k)=a(i,js(k)) a(i,js(k))=T end do end if end if !高斯消元法的核心变换 do i=k+1,n a(i,k)=a(i,k)/a(k,k) end do do i=k+1,n do j=k+1,n a(i,j)=a(i,j)-a(i,k)*a(k,j) end do b(i)=b(i)-a(i,k)*b(k) end do end do loop ! 结束最外层循环 ! 回代 x(n)=b(n)/a(n,n) do i=n-1,1,-1 T=0 do j=i+1,n T=T+a(i,j)*x(j) enddo x(i)=(b(i)-T)/a(i,i) enddo ! 由于在全主元法中进行了列变换，所以最后应对x（i）进行对应的调整 do k=n-1,1,-1 if (js(k) /= k) then T=x(k) x(k)=x(js(k)) x(js(k))=T endif enddo end