SECANT

 !Program name: SECANT

!Function: x^3+x-3

!Initial x values are 0 and 3.0

!Tolerance 1E-06

!Root=1.2134118

 

Real :: x0, x1, x2, xn, c

Real :: tolx

integer :: i

 

f(x)=x**3+x-3

 

tolx=1.E-06

x1=0.

x2=3.

 

write (*,5) "iter", "x1", "x2","y1","y2","c","xn-x0"

5  format (a5X,a10X,a20X,a20X,a15X, a15X,a15X,a15x)

do i=0,100

         x0=(x1*f(x2)-x2*f(x1))/(f(x2)-f(x1))

         c=f(x1)*f(x0)

         x1=x2

         x2=x0

         xn=(x1*f(x2)-x2*f(x1))/(f(x2)-f(x1))

    print *,i, x1, x2, f(x1), f(x2), c, xn-x0

       if (c == 0.) exit

       if (abs(xn-x0) .gt. tolx) cycle

       if (abs(xn-x0) .lt. tolx) exit

end do

    Print *, "The root of the equation is: ", x0

stop

end

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