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analysis.special_functions.complex.arg

The argument of a complex number. #

We define arg : ℂ → ℝ, returing a real number in the range (-π, π], such that for x ≠ 0, sin (arg x) = x.im / x.abs and cos (arg x) = x.re / x.abs, while arg 0 defaults to 0

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noncomputable def complex.arg (x : ℂ) :
ℝ

arg returns values in the range (-π, π], such that for x ≠ 0, sin (arg x) = x.im / x.abs and cos (arg x) = x.re / x.abs, arg 0 defaults to 0

Equations
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theorem complex.sin_arg (x : ℂ) :
real.sin x.arg = x.im / complex.abs x
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theorem complex.cos_arg {x : ℂ} (hx : x ≠ 0) :
real.cos x.arg = x.re / complex.abs x
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@[simp]
theorem complex.abs_mul_exp_arg_mul_I (x : ℂ) :
(↑(complex.abs x)) * complex.exp ((↑(x.arg)) * complex.I) = x
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@[simp]
theorem complex.abs_mul_cos_add_sin_mul_I (x : ℂ) :
(↑(complex.abs x)) * (complex.cos ↑(x.arg) + (complex.sin ↑(x.arg)) * complex.I) = x
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@[simp]
theorem complex.range_exp_mul_I  :
set.range (λ (x : ℝ), complex.exp ((↑x) * complex.I)) = metric.sphere 0 1
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theorem complex.arg_mul_cos_add_sin_mul_I {r : ℝ} (hr : 0 < r) {θ : ℝ} (hθ : θ ∈ set.Ioc (-real.pi) real.pi) :
((↑r) * (complex.cos ↑θ + (complex.sin ↑θ) * complex.I)).arg = θ
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theorem complex.arg_cos_add_sin_mul_I {θ : ℝ} (hθ : θ ∈ set.Ioc (-real.pi) real.pi) :
(complex.cos ↑θ + (complex.sin ↑θ) * complex.I).arg = θ
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@[simp]
theorem complex.arg_zero  :
0.arg = 0
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theorem complex.ext_abs_arg {x y : ℂ} (h₁ : complex.abs x = complex.abs y) (h₂ : x.arg = y.arg) :
x = y
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theorem complex.ext_abs_arg_iff {x y : ℂ} :
x = y ↔ complex.abs x = complex.abs y ∧ x.arg = y.arg
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theorem complex.arg_mem_Ioc (z : ℂ) :
z.arg ∈ set.Ioc (-real.pi) real.pi
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@[simp]
theorem complex.range_arg  :
set.range complex.arg = set.Ioc (-real.pi) real.pi
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theorem complex.arg_le_pi (x : ℂ) :
x.arg ≤ real.pi
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theorem complex.neg_pi_lt_arg (x : ℂ) :
-real.pi < x.arg
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@[simp]
theorem complex.arg_nonneg_iff {z : ℂ} :
0 ≤ z.arg ↔ 0 ≤ z.im
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@[simp]
theorem complex.arg_neg_iff {z : ℂ} :
z.arg < 0 ↔ z.im < 0
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theorem complex.arg_real_mul (x : ℂ) {r : ℝ} (hr : 0 < r) :
((↑r) * x).arg = x.arg
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theorem complex.arg_eq_arg_iff {x y : ℂ} (hx : x ≠ 0) (hy : y ≠ 0) :
x.arg = y.arg ↔ (↑(complex.abs y) / ↑(complex.abs x)) * x = y
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@[simp]
theorem complex.arg_one  :
1.arg = 0
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@[simp]
theorem complex.arg_neg_one  :
(-1).arg = real.pi
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@[simp]
theorem complex.arg_I  :
complex.I.arg = real.pi / 2
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@[simp]
theorem complex.arg_neg_I  :
(-complex.I).arg = -(real.pi / 2)
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@[simp]
theorem complex.tan_arg (x : ℂ) :
real.tan x.arg = x.im / x.re
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theorem complex.arg_of_real_of_nonneg {x : ℝ} (hx : 0 ≤ x) :
↑x.arg = 0
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theorem complex.arg_eq_pi_iff {z : ℂ} :
z.arg = real.pi ↔ z.re < 0 ∧ z.im = 0
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theorem complex.arg_of_real_of_neg {x : ℝ} (hx : x < 0) :
↑x.arg = real.pi
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theorem complex.arg_eq_pi_div_two_iff {z : ℂ} :
z.arg = real.pi / 2 ↔ z.re = 0 ∧ 0 < z.im
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theorem complex.arg_eq_neg_pi_div_two_iff {z : ℂ} :
z.arg = -(real.pi / 2) ↔ z.re = 0 ∧ z.im < 0
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theorem complex.arg_of_re_nonneg {x : ℂ} (hx : 0 ≤ x.re) :
x.arg = real.arcsin (x.im / complex.abs x)
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theorem complex.arg_of_re_neg_of_im_nonneg {x : ℂ} (hx_re : x.re < 0) (hx_im : 0 ≤ x.im) :
x.arg = real.arcsin ((-x).im / complex.abs x) + real.pi
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theorem complex.arg_of_re_neg_of_im_neg {x : ℂ} (hx_re : x.re < 0) (hx_im : x.im < 0) :
x.arg = real.arcsin ((-x).im / complex.abs x) - real.pi
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theorem complex.arg_of_im_nonneg_of_ne_zero {z : ℂ} (h₁ : 0 ≤ z.im) (h₂ : z ≠ 0) :
z.arg = real.arccos (z.re / complex.abs z)
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theorem complex.arg_of_im_pos {z : ℂ} (hz : 0 < z.im) :
z.arg = real.arccos (z.re / complex.abs z)
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theorem complex.arg_of_im_neg {z : ℂ} (hz : z.im < 0) :
z.arg = -real.arccos (z.re / complex.abs z)
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theorem complex.arg_conj (x : ℂ) :
(⇑conj x).arg = ite (x.arg = real.pi) real.pi (-x.arg)
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theorem complex.arg_inv (x : ℂ) :
x⁻¹.arg = ite (x.arg = real.pi) real.pi (-x.arg)
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@[simp]
theorem complex.arg_conj_coe_angle (x : ℂ) :
↑((⇑conj x).arg) = -↑(x.arg)
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@[simp]
theorem complex.arg_inv_coe_angle (x : ℂ) :
↑(x⁻¹.arg) = -↑(x.arg)
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theorem complex.arg_neg_eq_arg_sub_pi_of_im_pos {x : ℂ} (hi : 0 < x.im) :
(-x).arg = x.arg - real.pi
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theorem complex.arg_neg_eq_arg_add_pi_of_im_neg {x : ℂ} (hi : x.im < 0) :
(-x).arg = x.arg + real.pi
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theorem complex.arg_neg_eq_arg_sub_pi_iff {x : ℂ} :
(-x).arg = x.arg - real.pi ↔ 0 < x.im ∨ x.im = 0 ∧ x.re < 0
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theorem complex.arg_neg_eq_arg_add_pi_iff {x : ℂ} :
(-x).arg = x.arg + real.pi ↔ x.im < 0 ∨ x.im = 0 ∧ 0 < x.re
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theorem complex.arg_neg_coe_angle {x : ℂ} (hx : x ≠ 0) :
↑((-x).arg) = ↑(x.arg) + ↑real.pi
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theorem complex.arg_eq_nhds_of_re_pos {x : ℂ} (hx : 0 < x.re) :
complex.arg =ᶠ[𝓝 x] λ (x : ℂ), real.arcsin (x.im / complex.abs x)
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theorem complex.arg_eq_nhds_of_re_neg_of_im_pos {x : ℂ} (hx_re : x.re < 0) (hx_im : 0 < x.im) :
complex.arg =ᶠ[𝓝 x] λ (x : ℂ), real.arcsin ((-x).im / complex.abs x) + real.pi
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theorem complex.arg_eq_nhds_of_re_neg_of_im_neg {x : ℂ} (hx_re : x.re < 0) (hx_im : x.im < 0) :
complex.arg =ᶠ[𝓝 x] λ (x : ℂ), real.arcsin ((-x).im / complex.abs x) - real.pi
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theorem complex.arg_eq_nhds_of_im_pos {z : ℂ} (hz : 0 < z.im) :
complex.arg =ᶠ[𝓝 z] λ (x : ℂ), real.arccos (x.re / complex.abs x)
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theorem complex.arg_eq_nhds_of_im_neg {z : ℂ} (hz : z.im < 0) :
complex.arg =ᶠ[𝓝 z] λ (x : ℂ), -real.arccos (x.re / complex.abs x)
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theorem complex.continuous_at_arg {x : ℂ} (h : 0 < x.re ∨ x.im ≠ 0) :
continuous_at complex.arg x
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theorem complex.tendsto_arg_nhds_within_im_neg_of_re_neg_of_im_zero {z : ℂ} (hre : z.re < 0) (him : z.im = 0) :
filter.tendsto complex.arg (𝓝[{z : ℂ | z.im < 0}] z) (𝓝 (-real.pi))
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theorem complex.continuous_within_at_arg_of_re_neg_of_im_zero {z : ℂ} (hre : z.re < 0) (him : z.im = 0) :
continuous_within_at complex.arg {z : ℂ | 0 ≤ z.im} z
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theorem complex.tendsto_arg_nhds_within_im_nonneg_of_re_neg_of_im_zero {z : ℂ} (hre : z.re < 0) (him : z.im = 0) :
filter.tendsto complex.arg (𝓝[{z : ℂ | 0 ≤ z.im}] z) (𝓝 real.pi)