FinMatrix.CoqExt.RExt.RExtLt


Require Export RExtBase RExtSqr RExtAbs.

Basic automation


#[export] Hint Resolve
  Rlt_gt
  Rgt_lt
  Rle_ge
  Rlt_le
  Rge_le
  Rplus_lt_le_0_compat
  Rplus_le_lt_0_compat
  Rplus_lt_0_compat
  Rplus_le_le_0_compat
  Rsqr_pos_lt
  Rinv_0_lt_compat
  Rinv_lt_0_compat
  : R.

Additional properties

For arithmetic operations

0 <= 1
Lemma zero_le_1 : 0 <= 1.
Proof. ra. Qed.
#[export] Hint Resolve zero_le_1 : R.

a <> b -> a <= b -> a < b
Lemma Rneq_le_lt : forall a b, a <> b -> a <= b -> a < b.
Proof. ra. Qed.
#[export] Hint Resolve Rneq_le_lt : R.

a < b -> 0 < b - a
Lemma Rlt_Rminus : forall a b : R, a < b -> 0 < b - a.
Proof. intros. apply (proj2 (Rlt_0_minus a b)); auto. Qed.
#[export] Hint Resolve Rlt_Rminus : R.

0 < r -> 0 < 1 / r
Lemma Rinv1_gt0 : forall r : R, 0 < r -> 0 < 1 / r.
Proof. ra. unfold Rdiv; ra. Qed.
#[export] Hint Resolve Rinv1_gt0 : R.

0 <= a -> b < 0 -> a / b <= 0
Lemma Rdiv_ge0_lt0_le0 : forall a b : R, 0 <= a -> b < 0 -> a / b <= 0.
Proof. ra. assert (/b < 0); ra. Qed.
#[export] Hint Resolve Rdiv_ge0_lt0_le0 : R.

a < 0 -> b < 0 -> 0 < a / b
Lemma Rdiv_gt0_compat_neg : forall a b : R, a < 0 -> b < 0 -> 0 < a / b.
Proof. ra. assert (/b < 0); ra. Qed.
#[export] Hint Resolve Rdiv_gt0_compat_neg : R.

0 <= a -> 0 < b -> 0 <= a / b
Lemma Rdiv_ge0_compat : forall a b : R, 0 <= a -> 0 < b -> 0 <= a / b.
Proof. ra. assert (0 < /b); ra. Qed.
#[export] Hint Resolve Rdiv_ge0_compat : R.

0 < a -> b < 0 -> a / b < 0
Lemma Rdiv_lt_0_compat_l : forall a b : R, 0 < a -> b < 0 -> a / b < 0.
Proof. intros. unfold Rdiv. assert (/b < 0); ra. Qed.
#[export] Hint Resolve Rdiv_lt_0_compat_l : R.

a < 0 -> 0 < b -> a / b < 0
Lemma Rdiv_lt_0_compat_r : forall a b : R, a < 0 -> 0 < b -> a / b < 0.
Proof. intros. unfold Rdiv. assert (/b > 0); ra. Qed.
#[export] Hint Resolve Rdiv_lt_0_compat_r : R.

0 <= a² + b²
Lemma Rplus2_sqr_ge0 : forall a b : R, 0 <= a² + b².
Proof. ra. Qed.
#[export] Hint Resolve Rplus2_sqr_ge0 : R.

a² + b² <> 0 -> 0 < a² + b²
Lemma Rplus2_sqr_neq0_imply_gt0 : forall a b : R, a² + b² <> 0 -> 0 < a² + b².
Proof. ra. Qed.
#[export] Hint Resolve Rplus2_sqr_neq0_imply_gt0 : R.

0 < a² + b² -> a² + b² <> 0
Lemma Rplus2_sqr_neq0_if_gt0 : forall a b : R, 0 < a² + b² -> a² + b² <> 0.
Proof. ra. Qed.
#[export] Hint Resolve Rplus2_sqr_neq0_if_gt0 : R.

a² + b² <> 0 <-> 0 < a² + b²
Lemma Rplus2_sqr_neq0_iff_gt0 : forall a b : R, a² + b² <> 0 <-> 0 < a² + b².
Proof. ra. Qed.

2 * a * b <= a² + b²
Lemma R_neq1 : forall a b : R, 2 * a * b <= a² + b².
Proof. intros. apply Rge_le. apply Rminus_ge. rewrite <- Rsqr_minus. ra. Qed.
#[export] Hint Resolve R_neq1 : R.

0 < a² + b² -> (a <> 0 \/ b <> 0)
Lemma Rplus2_sqr_gt0_imply : forall a b : R, 0 < a² + b² -> (a <> 0 \/ b <> 0).
Proof. ra. Qed.
#[export] Hint Resolve Rplus2_sqr_gt0_imply : R.

(a <> 0 \/ b <> 0) -> 0 < a² + b²
Lemma Rplus2_sqr_gt0_if : forall a b : R, (a <> 0 \/ b <> 0) -> 0 < a² + b².
Proof. ra. Qed.
#[export] Hint Resolve Rplus2_sqr_gt0_if : R.

0 < a² + b² <-> (a <> 0 \/ b <> 0)
Lemma Rplus2_sqr_gt0 : forall a b : R, 0 < a² + b² <-> (a <> 0 \/ b <> 0).
Proof. ra. Qed.

a <> 0 -> 0 < a² + b²
Lemma Rplus2_sqr_gt0_l : forall a b, a <> 0 -> 0 < a² + b².
Proof. ra. Qed.
#[export] Hint Resolve Rplus2_sqr_gt0_l : R.

b <> 0 -> 0 < a² + b²
Lemma Rplus2_sqr_gt0_r : forall a b, b <> 0 -> 0 < a² + b².
Proof. ra. Qed.
#[export] Hint Resolve Rplus2_sqr_gt0_r : R.

(a * c + b * d)² <= (a² + b²) * (c² + d²)
Lemma Rsqr_mult_le : forall a b c d : R, (a * c + b * d)² <= (a² + b²) * (c² + d²).
Proof.
  intros. unfold Rsqr. ring_simplify.
  rewrite !associative. apply Rplus_le_compat_l.
  rewrite <- !associative. apply Rplus_le_compat_r.
  autorewrite with R.
  replace (a² * d²) with (a * d)²; [|ra].
  replace (c² * b²) with (c * b)²; [|ra].
  replace (2 * a * c * b * d) with (2 * (a * d) * (c * b)); [|ra].
  apply R_neq1.
Qed.

b > 0 -> a * /b < c -> a < b * c
Lemma Rdiv_le_imply_Rmul_gt a b c : b > 0 -> a * / b < c -> a < b * c.
Proof.
  ra. apply (Rmult_lt_compat_l b) in H0; auto.
  replace (b * (a * /b)) with a in H0; auto. ra.
Qed.
#[export] Hint Resolve Rdiv_le_imply_Rmul_gt : R.

b > 0 -> a < b * c -> a * / b < c
Lemma Rmul_gt_imply_Rdiv_le a b c : b > 0 -> a < b * c -> a * / b < c.
Proof.
  ra. apply (Rmult_lt_compat_l (/b)) in H0; auto with R.
  replace (/b * a) with (a / b) in *; ra.
  replace (/b * (b * c)) with c in *; ra.
Qed.
#[export] Hint Resolve Rmul_gt_imply_Rdiv_le : R.

0 < a -> 0 < b -> 0 < c -> a < b * c -> a / b < c
Lemma Rdiv_lt_gt0_gt0_gt0 : forall a b c : R,
    0 < a -> 0 < b -> 0 < c -> a < b * c -> a / b < c.
Proof. ra. unfold Rdiv; ra. Qed.
#[export] Hint Resolve Rdiv_lt_gt0_gt0_gt0 : R.

0 <= a -> 0 < b -> a <= b -> a / b <= 1
Lemma Rdiv_le_1 : forall x y : R, 0 <= x -> 0 < y -> x <= y -> x / y <= 1.
Proof.
  intros. unfold Rdiv. replace 1 with (y * / y); ra.
  apply Rmult_le_compat_r; ra.
Qed.

b <> 0 -> |a| <= |b| -> |a / b| <= 1
Lemma Rdiv_abs_le_1 : forall a b : R, b <> 0 -> |a| <= |b| -> | a / b | <= 1.
Proof.
  intros. unfold Rdiv. rewrite Rabs_mult. rewrite Rabs_inv.
  apply Rdiv_le_1; auto; ra. apply Rabs_pos_lt; auto.
Qed.

For operation sqrt

\sqrt {a² + b²} <= |a| + |b|
Lemma R_neq5 : forall a b : R, sqrt (a² + b²) <= Rabs a + Rabs b.
Proof.
  intros.
  rewrite <- sqrt_square.
  - apply sqrt_le_1_alt.
    apply Rle_trans with (Rabs a * Rabs a + Rabs b * Rabs b)%R.
    + rewrite <- !Rabs_mult. apply Rplus_le_compat.
      apply RRle_abs. apply RRle_abs.
    + ring_simplify.
      rewrite !Rplus_assoc. apply Rplus_le_compat_l.
      rewrite <- Rplus_0_l at 1. apply Rplus_le_compat_r.
      assert (0 <= Rabs a) by ra; assert (0 <= Rabs b) by ra. ra.
  - assert (0 <= Rabs a) by ra; assert (0 <= Rabs b) by ra. ra.
Qed.

a * c + b * d <= \sqrt {(a² + b²) * (c² + d²)}
Lemma R_neq6 : forall a b c d : R, a * c + b * d <= sqrt((a² + b²) * (c² + d²)).
Proof.
  intros.
  apply Rsqr_incr_0_var; ra.
  rewrite Rsqr_sqrt; ra.
  unfold Rsqr. ring_simplify.
  rewrite !Rplus_assoc; repeat apply Rplus_le_compat_l.
  rewrite <- !Rplus_assoc; repeat apply Rplus_le_compat_r.
  autorewrite with R.
  replace (2 * a * c * b * d) with (2 * (a * d) * (b * c)) by ra.
  replace (a² * d² + c² * b²)%R with ((a*d)² + (b * c)²) by ra.
  apply R_neq1.
Qed.

For famous inequalities




Lemma Rneq_AM_GM_2 : forall a b : R,
    0 <= a -> 0 <= b ->
    (a + b) / 2 >= sqrt(a * b).
Proof.
Admitted.

Lemma Rneq_AM_GM_3 : forall a b c : R,
    0 <= a -> 0 <= b -> 0 <= c ->
    (a + b + c) / 3 >= sqrt(a * b).
Admitted.

For inequalities about PI

0 < r -> 0 < r * PI
Lemma mult_PI_gt0 : forall r, 0 < r -> 0 < r * PI.
Proof. ra. Qed.

Section lra_problem.

  Variable abcdefg : R.
  Hypotheses Habcdefg : - PI < abcdefg < PI.


  Lemma Rsplit_neg_pi_to_pi' : forall a : R,
      -PI < a <= PI <->
        a = -PI/2 \/ a = 0 \/ a = PI/2 \/
          (-PI < a < -PI/2) \/ (-PI/2 < a < 0) \/
          (0 < a < PI/2) \/ (PI/2 < a <= PI).
  Proof.
    intros.
    lra.
  Qed.
End lra_problem.

Goal 2 < PI.
Proof.
Abort.

Explicit upper and lower bound of PI
Notation PI_ub := 3.14159266.
Notation PI_lb := 3.14159265.
Axiom PI_ub_axiom : PI < PI_ub.
Axiom PI_lb_axiom : PI_lb < PI.
#[export] Hint Resolve PI_ub_axiom PI_lb_axiom : R.

PI_lb < PI < PI_ub
Lemma PI_bound : PI_lb < PI < PI_ub.
Proof. ra. Qed.

Section test.
  Goal 2 < PI.
  Proof.
    ra. apply Rlt_trans with PI_lb; ra.
  Qed.

  Goal 2 < PI.
  Proof.
    pose proof PI_bound. ra.
  Qed.
End test.

Other things that need to be done manually


Section examples.

  Goal forall a b c, a > 0 -> b <= c / a -> 0 <= c - b *a.
  Proof.
    ra.
    apply Rmult_le_compat_r with (r:=a) in H0; ra.
    unfold Rdiv in H0. rewrite Rmult_assoc in H0.
    rewrite Rinv_l in H0; ra.
  Qed.



  Goal forall h T, 0 < h -> h < 9200 -> -60 < T -> T < 60 -> h / (273.15 + T) < 153.
  Proof. ra. Abort.

  Variable h T : R.
  Hypothesis Hh1 : 0 < h.
  Hypothesis Hh2 : h < 9200.
  Hypothesis HT1 : -60 < T.
  Hypothesis HT2 : T < 60.

  Goal h * 0.0065 < 273.15 + T. ra. Qed.

  Goal h / (273.15 + T) < 153.
  Proof.
    ra.
    assert (273.15 + T > 0); ra.
    assert (h < (273.15 + T) * 153); ra.
    unfold Rdiv; ra.
  Qed.

  Goal h / (273.15 + T) < 1 / 0.0065.
  Proof.
    ra.
    assert (273.15 + T > 0); ra.
    assert (h < (273.15 + T) * (1/0.0065)); ra.
    apply Rdiv_lt_gt0_gt0_gt0; ra.
  Qed.

  Goal 0 < 1 - (0.0065 * (h * / (273.15 + T))).
  Proof.
    assert (h / (273.15 + T) < /0.0065); ra.
    apply Rdiv_lt_gt0_gt0_gt0; ra.
  Qed.

End examples.

Extra automation