Noisy Data

program noisy_data
    implicit none
    integer, parameter:: n=6
    integer:: i, j, k
    real:: x(n), yd(n), f, s, m, p, q, p1, q1

    open(11, file="in.txt")

    do i=1,n
        read(11,*) x(i)
    end do

    do i=1,n
        read(11,*) yd(i)
    end do

    close(11)

    p1=1.0
    q1=-2.0
    s=0.0
    do i=1,n
        s=s+(f(x(i),p1,q1)-yd(i))**2
    end do
    m=s

    do p=1.0,3.0,0.1
        do q=-2.0,-1.0,0.1
            s=0.0
            do i=1,n
                s=s+(f(x(i),p,q)-yd(i))**2
            end do
            if(s<m) then
                m=s
                p1=p
                q1=q
            end if
        end do
    end do

    open(12, file="out.txt")
    write(12,13) m, p1, q1
    13 format("minimum value is ",f7.3," at p = ",f6.3," and q = ",f6.3)
    close(12)

end program noisy_data

function f(x, p, q) result(y)
    real:: x, y, p, q
    y=p+q*x
end function