#ifndef STAN_MATH_REV_FUN_STEP_HPP
#define STAN_MATH_REV_FUN_STEP_HPP

#include <stan/math/rev/meta.hpp>
#include <stan/math/rev/core.hpp>

namespace stan {
namespace math {

/**
 * Return the step, or heaviside, function applied to the
 * specified variable (stan).
 *
 * See step() for the double-based version.
 *
 * The derivative of the step function is zero everywhere
 * but at 0, so for convenience, it is taken to be everywhere
 * zero,
 *
 * \f$\mbox{step}(x) = 0\f$.
 *
 * @param a Variable argument.
 * @return The constant variable with value 1.0 if the argument's
 * value is greater than or equal to 0.0, and value 0.0 otherwise.
 */
inline var step(const var& a) {
  return var(new vari(a.vi_->val_ < 0.0 ? 0.0 : 1.0));
}

}  // namespace math
}  // namespace stan
#endif
