A_04 POWER METHOD, Fortran

A_04 POWER METHOD

PROGRAM Power_method
IMPLICIT NONE
INTEGER,PARAMETER::n=3
INTEGER::i,j,k,maxn,p
REAL:: mu,tol,norm
REAL,DIMENSION(n,n) :: a
REAL,DIMENSION(n) :: x,xn,y
Data a/-4.0,-5.0,-1.0,14.0,13.0,0.0,0.0,0.0,2.0/
Data x/1.0,1.0,1.0/
PRINT*,'ENTER THE VALUE OF MAXN:'
READ*,maxn
PRINT*,'ENTER THE VALUE OF TOL:'
READ*,tol

WRITE(*,*)'step          x1              x2           x3            mu'
    WRITE(*,*)0,(x(i),i=1,n)

DO k=1,maxn
        y=MATMUL(a,x)
       
        DO p=1,n
            IF(ABS(y(p))==MAXVAL(ABS(y))) EXIT
        END DO

IF(y(p)==0) THEN
            WRITE(*,*)'eigenvector ',x
            WRITE(*,*)'A has the eigenvalue = 0, we have to choose  a new vector x and restart.'
            STOP
        END IF
        mu=y(p)
        xn=y/y(p)
        norm=MAXVAL(ABS(x-xn))
        x=xn

WRITE(*,*)k,(x(i),i=1,n),mu

IF(norm<tol)THEN
            WRITE(*,*)"Dominant Eigenvalue =",mu
            
            STOP
        END IF

END DO
    WRITE(*,*)' Iteration exceeded.'
END PROGRAM Power_method


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