A_04 POWER METHOD, Fortran

A_04 POWER METHOD

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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

Show compiler warnings [ - ] Show input
Compilation time: 0.29 sec, absolute running time: 0.16 sec, cpu time: 0.01 sec, memory peak: 5 Mb, absolute service time: 2,38 sec

ENTER THE VALUE OF MAXN: ENTER THE VALUE OF TOL: step x1 x2 x3 mu 0 1.00000000 1.00000000 1.00000000 1 1.00000000 0.800000012 0.100000001 10.0000000 2 1.00000000 0.750000000 -0.111111112 7.20000029 3 1.00000000 0.730769217 -0.188034192 6.50000000 4 1.00000000 0.722222209 -0.220850483 6.23076916 5 1.00000000 0.718181849 -0.235914722 6.11111069 6 1.00000000 0.716216207 -0.243094936 6.05454588 7 1.00000000 0.715246558 -0.246587545 6.02702713 8 1.00000000 0.714765131 -0.248305827 6.01345158 9 1.00000000 0.714525163 -0.249156550 6.00671196 10 1.00000000 0.714405358 -0.249579400 6.00335217 11 1.00000000 0.714345515 -0.249790072 6.00167513 12 1.00000000 0.714315653 -0.249895155 6.00083733 13 1.00000000 0.714300632 -0.249947593 6.00041914 14 1.00000000 0.714293182 -0.249973834 6.00020885 15 1.00000000 0.714289486 -0.249986932 6.00010443 16 1.00000000 0.714287579 -0.249993443 6.00005293 Dominant Eigenvalue = 6.00005293