text: #include <stan/math/mix/scal.hpp>
  #include <gtest/gtest.h>
  #include <math/rev/scal/util.hpp>
  #include <math/mix/scal/fun/nan_util.hpp>
  
  TEST(AgradFwdLog2, FvarVar_1stDeriv) {
    using stan::math::fvar;
    using stan::math::var;
    using std::log;
  
    fvar<var> x(0.5, 1.3);
    fvar<var> a = log2(x);
  
    EXPECT_FLOAT_EQ(log2(0.5), a.val_.val());
    EXPECT_FLOAT_EQ(1.3 / (0.5 * log(2)), a.d_.val());
  
    AVEC y = createAVEC(x.val_);
    VEC g;
    a.val_.grad(y, g);
    EXPECT_FLOAT_EQ(1 / (0.5 * log(2)), g[0]);
  }
  TEST(AgradFwdLog2, FvarVar_2ndDeriv) {
    using stan::math::fvar;
    using stan::math::var;
    using std::log;
  
    fvar<var> x(0.5, 1.3);
    fvar<var> a = log2(x);
  
    AVEC y = createAVEC(x.val_);
    VEC g;
    a.d_.grad(y, g);
    EXPECT_FLOAT_EQ(-1.3 / (0.25 * log(2)), g[0]);
  }
  TEST(AgradFwdLog2, FvarFvarVar_1stDeriv) {
    using stan::math::fvar;
    using stan::math::var;
    using std::log;
  
    fvar<fvar<var> > x;
    x.val_.val_ = 0.5;
    x.val_.d_ = 1.0;
  
    fvar<fvar<var> > a = log2(x);
  
    EXPECT_FLOAT_EQ(log2(0.5), a.val_.val_.val());
    EXPECT_FLOAT_EQ(1 / (0.5 * log(2)), a.val_.d_.val());
    EXPECT_FLOAT_EQ(0, a.d_.val_.val());
    EXPECT_FLOAT_EQ(0, a.d_.d_.val());
  
    AVEC p = createAVEC(x.val_.val_);
    VEC g;
    a.val_.val_.grad(p, g);
    EXPECT_FLOAT_EQ(1.0 / (0.5 * log(2)), g[0]);
  
    fvar<fvar<var> > y;
    y.val_.val_ = 0.5;
    y.d_.val_ = 1.0;
  
    fvar<fvar<var> > b = log2(y);
    EXPECT_FLOAT_EQ(log2(0.5), b.val_.val_.val());
    EXPECT_FLOAT_EQ(0, b.val_.d_.val());
    EXPECT_FLOAT_EQ(1 / (0.5 * log(2)), b.d_.val_.val());
    EXPECT_FLOAT_EQ(0, b.d_.d_.val());
  
    AVEC q = createAVEC(y.val_.val_);
    VEC r;
    b.val_.val_.grad(q, r);
    EXPECT_FLOAT_EQ(1.0 / (0.5 * log(2)), r[0]);
  }
  TEST(AgradFwdLog2, FvarFvarVar_2ndDeriv) {
    using stan::math::fvar;
    using stan::math::var;
    using std::log;
  
    fvar<fvar<var> > x;
    x.val_.val_ = 0.5;
    x.val_.d_ = 1.0;
  
    fvar<fvar<var> > a = log2(x);
  
    AVEC p = createAVEC(x.val_.val_);
    VEC g;
    a.val_.d_.grad(p, g);
    EXPECT_FLOAT_EQ(-1.0 / (0.25 * log(2)), g[0]);
  
    fvar<fvar<var> > y;
    y.val_.val_ = 0.5;
    y.d_.val_ = 1.0;
  
    fvar<fvar<var> > b = log2(y);
  
    AVEC q = createAVEC(y.val_.val_);
    VEC r;
    b.d_.val_.grad(q, r);
    EXPECT_FLOAT_EQ(-1.0 / (0.5 * 0.5 * log(2)), r[0]);
  }
  TEST(AgradFwdLog2, FvarFvarVar_3rdDeriv) {
    using stan::math::fvar;
    using stan::math::var;
  
    fvar<fvar<var> > x;
    x.val_.val_ = 0.5;
    x.val_.d_ = 1.0;
    x.d_.val_ = 1.0;
  
    fvar<fvar<var> > a = log2(x);
  
    AVEC p = createAVEC(x.val_.val_);
    VEC g;
    a.d_.d_.grad(p, g);
    EXPECT_FLOAT_EQ(23.0831206542234145177587948960, g[0]);
  }
  
  struct log2_fun {
    template <typename T0>
    inline T0 operator()(const T0& arg1) const {
      return log2(arg1);
    }
  };
  
  TEST(AgradFwdLog2, log2_NaN_1) {
    log2_fun log2_;
    test_nan_mix(log2_, false);
  }
  