Interface n_test_gradient

Test a function against its gradient by evaluating the gradient from the function by symmetric finite differnces. We can only test the gradient if energy and force functions are pure in that they do not change the input vector (e.g. no capping of parameters). The interface for func(x) and dfunc(x)are the same as for minim above.

xx -- real(dp), intent(in), dimension(:)

Position

dir -- real(dp), intent(in), optional, target, dimension(:)

direction along which to test

Function func(x) -- real(dp)

x -- real(dp), dimension(:)

Function dfunc(x) -- real(dp), dimension(size(x))

x -- real(dp), dimension(:)

n_linmin subroutine