Sffgg, Fortran - rextester

Sffgg

! Creating a program to solve a numerical set by using Gauss elimination method(backward substitution)
  Real a(10,10),b(10),x(10),pivot,sum
  Integer i,j,k,n,p
  WRITE(*,*)'Insert here the dimension of the matrix'
   Read(*,*)n
  Write(*,*)'Insert here the coefficients of the given equations in matrix form,also insert the values row wise'
  Do i=1,n
   Read(*,*)(a(i,j),j=1,n),b(i)     !read the matrix
    End do
       Write(*,*)'So, the matrix form by the given coefficients of those equations is as follows'
   Do i=1,n                   ! Write the matrix
    WRITE(*,*) (a(i,j),j=1,n)
    End do
     Write(*,*)'hence the B vector will be is'
      Do i=1,n
      Write(*,*)b(i)
      End do
    Do i=1,n     !loop begins for gauss elimination (backward elimination)
   max=abs(a(i,i))  !pivoting start right here
   d=i
   Do j=i+1,n
  If(abs(a(j,i)).gt.max)then
    max=abs(a(j,i))
   p=j
   Do k=1,n       !  interchanging rows
   temp1=a(p,k)
   a(p,k)=a(d,k)
   a(d,k)=temp1
   End do
   temp2=b(p)
  b(p)=b(d)
  b(d)=temp2
  pivot=a(p,d)/a(d,d)
  Do k=1,n
   a(p,k)=a(p,k)-pivot*a(d,k)
   End do
   b(p)=b(p)-pivot*b(d)
   Else
   pivot=a(j,d)/a(d,d)
    do k=1,n
   a(j,k)=a(j,k)-pivot*a(d,k)
   End do
   b(j)=b(j)-pivot*b(d)
  End if
   End do
   End do
   Write(*,*)'so, the triangular matrix after gauss elimination will be :'
     Do i=1,n
  Write(*,*)(a(i,j),j=1,n)
    End do
   Write(*,*)'therefore, the corresponding vector B is:'
    Do i=1,n
    Write(*,*)b(i)
    End do
    Do i=n,1,-1   !back substitution
  sum=0.0
  Do j=i+1,n
   sum=sum+a(i,j)*x(j)
   End do
    x(i)=(b(i)-sum)/a(i,i)
   End do
Write(*,*)'SO, THE SOLUTIONS OF THE GIVEN LINEAR EQUATIONS ARE :'
   Do i=1,n
    WRITE(*,10)i,x(i)
  End do
10  format('X(',I3,')=',f10.5)
Stop
End


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