inv_square.hpp

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#ifndef STAN_MATH_REV_FUN_INV_SQUARE_HPP
#define STAN_MATH_REV_FUN_INV_SQUARE_HPP
 
#include <stan/math/rev/meta.hpp>
#include <stan/math/rev/core.hpp>
#include <stan/math/prim/fun/inv_square.hpp>
 
namespace stan {
namespace math {
 
inline var inv_square(const var& a) {
  auto a_cube = a.val() * a.val() * a.val();
  return make_callback_var(inv_square(a.val()), [a, a_cube](auto& vi) mutable {
    a.adj() -= 2 * vi.adj() / a_cube;
  });
}
 
}  // namespace math
}  // namespace stan
#endif