tasks a-s

Task/Nth-root/Fortran/nth-root.f

@@ -0,0 +1,42 @@
+program NthRootTest
+  implicit none
+
+  print *, nthroot(10, 7131.5**10)
+  print *, nthroot(5, 34.0)
+
+contains
+
+  function nthroot(n, A, p)
+    real :: nthroot
+    integer, intent(in)        :: n
+    real, intent(in)           :: A
+    real, intent(in), optional :: p
+
+    real :: rp, x(2)
+
+    if ( A < 0 ) then
+       stop "A < 0"       ! we handle only real positive numbers
+    elseif ( A == 0 ) then
+       nthroot = 0
+       return
+    end if
+
+    if ( present(p) ) then
+       rp = p
+    else
+       rp = 0.001
+    end if
+
+    x(1) = A
+    x(2) = A/n   ! starting "guessed" value...
+
+    do while ( abs(x(2) - x(1)) > rp )
+       x(1) = x(2)
+       x(2) = ((n-1.0)*x(2) + A/(x(2) ** (n-1.0)))/real(n)
+    end do
+
+    nthroot = x(2)
+
+  end function nthroot
+
+end program NthRootTest