Hanoi University of Science and Technology
Question
Asked 26th Jul, 2023
Is there any mathematical tool or other efficient way to transform from component form to vector form of partial differential equation?
In the field of solid mechanics, Navier’s partial differential equation of linear elasticity for material in vector form is:
(λ+G)∇(∇⋅f) + G∇2f = 0, where f = (u, v, w)
The corresponding component form can be evaluated by expanding the ∇ operator and organizing it as follows:
For x-component (u):
(λ+2G)*∂2u/∂x2 + G*(∂2u/∂y2 + ∂2u/∂z2) + (λ+G)*(∂2v/(∂x∂y) + ∂2v/(∂x∂z)) = 0
However, I find it difficult to convert from the component form back to its compact vector form using the combination of divergence, gradient, and Laplacian operators, especially when there are coefficients involved.
Does anyone have any experience with this? Any advice would be appreciated.
All Answers (2)
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Does someone have any idea for proving or rejecting the Riemann Hypothesis?
Shitephen Wang
Does someone have any idea for proving or rejecting the Riemann Hypothesis?
Mathematical proof of Euler product
ζ(s) = Σ 1/n^s = 1/1^s + 1/2^s + 1/3^s + ... ... + 1/n^s -----[1]
s>=1, ζ(S) divergent
1/2^s ζ(S) = 1/2^s + 1/4^s + 1/6^s + ... ... + 1/2n^s -----[2]
[1]-[2]
=> (1-1/2^s) ζ(S) = 1 + 1/3^s + 1/5^s + 1/7^s + ... ... -----[3]
1/3^s (1-1/2^s) ζ(S) = 1/3^s + 1/9^s + 1/15^s + 1/21^s + ... ... -----[4]
[3]-[4]
=> (1-1/3^s) (1-1/s^s) ζ(S) = 1 + 1/5^s + 1/7^s + 1/11^s + 1/13^s + ... ...
... ...
(1-1/5^s)(1-1/3^s)(1-1/2^s) ζ(S) = 1 + 1/7^s + 1/11^s + 1/13^s + ... ...
... ...
∏(1-1/p^s) ζ(S) = 1
p(prime numbers)
=> ζ(S) = ∏(1-1/p^s)^(-1) = 1/1^s + 1/2^s + 1/3^s + ... ... + 1/n^s
s=1, ζ(S) divergent
So prime numbers are infinitas
Euler product is only meaningful when s>=1; the output will diverge if s<1
Riemann used analytic continuation to make the ζ(s) function meaningful on the complex plane
when s<1.
ζ(s) = Σ 1/n^s = 1/1^s + 1/2^s + 1/3^s + ... ... + 1/n^s
analytic continuation -∞ <= s <= ∞
=> ζ(s) = Γ(1-s)/2𝝅i * ∫{-∞}^[∞] [(-Z)^s / (e^z - 1)] dZ/Z = Reimann ζ function (s)
Reimann ζ(s) = Σ 1/n^s, s∈C, n∈N
where s is any complex number, while n is any natural number.
Γ(s)= (s-1)!
ζ(s) = 2Γ(1-s)/(2𝝅)^(s-1) * sin (𝝅s/2) ζ(1-s)
when s = -2, -4, -6 ... ...
ζ(s) = 0 (trivial zeros)
Reimann hypothesis (1859)
all nontrivial zeros of ζ(s) function, their output of complex number with real part 1/2.
# Original paper here ----- https://www.emis.de/classics/Riemann/Zeta.pdf
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