bissection.f90

program Lista01_Q09

implicit none

integer, parameter  :: prec9 = selected_real_kind(p=9)
real (kind=prec9)   :: root, bissecMethod, falsaPosMethod, a, b

print   *, 'Entre com o inicio e fim do intervalo'
read    *, a, b

root = bissecMethod(a, b)

print *, 'Com o metodo da bisseccao', root

root = falsaPosMethod(a, b)

print *, 'Com o metodo da falsa posicao', root

end program

function f(x)
    implicit none

    integer, parameter  :: prec9 = selected_real_kind(p=9)
    real (kind = prec9) :: f, x

    f = cos(x) + 1 - x
end function f

function bissecMethod(a, b)
    implicit none

    integer, parameter  :: prec9 = selected_real_kind(p=9)
    real (kind = prec9) :: intervalIni, intervalEnd, c, fcVal, f, bissecMethod, a, b
    integer               :: i

    intervalIni = a
    intervalEnd = b

    do i = 1, 100
        c = (intervalIni + intervalEnd) / 2

    fcVal = f(c)

        if(abs(fcVal) < 0.00000001) then
            exit
        end if

        if(f(a) < 0.0) then
        if(fcVal < 0.0) then
            intervalIni = c
                else
            intervalEnd = c
                end if
        else
        if(fcVal < 0) then
            intervalEnd = c
                else
            intervalIni = c
                end if
        end if
    end do

    bissecMethod = c
end function bissecMethod

function falsaPosMethod(a, b)
    implicit none

    integer, parameter  :: prec9 = selected_real_kind(p=9)
    real (kind = prec9) :: intervalIni, intervalEnd, c, fcVal, faVal, fbVal, f, falsaPosMethod, a, b
    integer             :: i

    intervalIni = a
    intervalEnd = b

    do i = 1, 100
        faVal = f(intervalIni)
        fbVal = f(intervalEnd)

        c = intervalEnd - fbVal * (intervalEnd - intervalIni) / (fbVal - faVal)

        fcVal = f(c)

        if(abs(fcVal) < 0.00000001) then
            exit
        end if

        if(f(a) < 0.0) then
        if(fcVal < 0.0) then
            intervalIni = c
                else
            intervalEnd = c
                end if
        else
        if(fcVal < 0) then
            intervalEnd = c
                else
            intervalIni = c
                end if
        end if
    end do

    falsaPosMethod = c
end function falsaPosMethod