# Questions tagged [mathematical-physics]

DO NOT USE THIS TAG for elementary physical questions. This tag is intended for questions on modern mathematical methods used in quantum theory, general relativity, string theory, integrable system etc at an advanced undergraduate or graduate level.

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0answers
11 views

### Engineering question about magnitude in terms of frequency

How do I calculate magnitude of Vout/Vin as a function of w (frequency) when given the resistor and capacitive values?
0answers
59 views

### Is algebraic geometry actually used in string theory?

Many times I have heard string theorists say that string theory has a lot of algebraic geometry, but physicists seem to have identified complex differential geometry with algebraic geometry and ...
0answers
29 views

### How can I solve this PDE in cylindrical coordinates?

I got the following equation from physics. $$C \sin \theta \frac{\partial T}{\partial \theta} = \frac{1}{r} \frac{\partial }{\partial r} \left( r \frac{\partial T}{\partial r} \right)$$ where ...
1answer
59 views

### How to solve this integral of an ODE?

https://www.symbolab.com/solver/integral-calculator/%5Cint%5Cint%5Cleft(Ax%5E%7B2%7D%2B%5Cfrac%7BB%7D%7Bx%7D%2B%5Cfrac%7B2%7D%7Bx%5E%7B2%7D%7D%5Cright)dxdx I have used this symbolic solver to solve ...
1answer
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### How to reduce differential operator to a 4th order ODE of the standard Euler type?

I read this article https://mae.ufl.edu/~uhk/STOKES-DRAG-FORMULA.pdf How do we actually arrive to a 4th order ODE below?
0answers
48 views

### Poincaré bundle, a way of understanding it.

So I will call the Poincaré bundle $(FM,\pi, M)$ the principal fiber bundle that has the Poincaré group as a structure group, the space of linear frames as total space and M as the Riemann-Cartan ...
0answers
36 views

### Road map Like github [closed]

Can someone create map like application for physics and mathematics like Github is for software. It is a mess at the moment.
4answers
95 views

### Is this workaround used by my book to find the value of $1/0$ legitimate?

I was doing a physics problem and found that I reached an interesting equation: Question To cross the river directly from A to B (making a right angle with the velocity of the stream), how must the ...
0answers
90 views

### Is this workaround used by my book to find the value of $1/0$ legitimate? [duplicate]

I was doing a physics problem and found that I reached an interesting equation:- To cross the river directly from A to B (making a right angle with the velocity of the stream), how must the fisherman ...
0answers
154 views

2answers
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### Any software recommendations to draw such graphs? [closed]

I am looking any alternatives software to draw similar graph images i posted here.
1answer
56 views

### Constructing a connection $1$-form from local forms.

I am following Section $10.1.3$ of Geometry, Topology and Physics by Nakahara, and have ran in to an issue regarding local connection forms. Consider a principal $G$-bundle, $P(M,G)$, and an open ...
0answers
32 views

### Logarithm term in “light-cone” operator expansion

I'm cross-posting from Physics site here because I don't know where this question fits better. I'm trying to understand how the logarithm in eq. (3.25) from this paper appears from the equation above ...
1answer
17 views

### Calculate the angle between a vector and a gravity pendulum

There is a physical device (sensor) which I can rotate. The device sends its X Y Z coordinates and a calculated acceleration vector in mg (mill mg). For example: X 116.0 Y 98.0 Z 151.0 MG 1031.0 X 117....
0answers
27 views

### Integrating an exponential containing a cosine function $\int_0^{2\pi} e^{i \nu \theta \pm ix\cos(\theta-\theta_0)} d \theta$

I'm trying to integrate $\int_0^{2\pi} e^{i \nu \theta \pm ix\cos(\theta-\theta_0)} d \theta$. According to a reference from the Journal of Mathematical Physics (https://doi.org/10.1063/1.5108599), ...
0answers
35 views

### Density and dimensionality of zeros in inverse square force fields of randomly distributed + and - charges in (at least) 1, 2 and 3 dimensions?

@mlk's answer to Density and dimensionality of zeros in inverse square force fields of randomly distributed sources in (at least) 1, 2 and 3 dimensions? is pleasing and straightforward, switching to ...
1answer
645 views

### Density and dimensionality of zeros in inverse square force fields of randomly distributed sources in (at least) 1, 2 and 3 dimensions?

Background: In this answer to Are there places in the Universe without gravity? in Astronomy SE I did a quick finite 2D calculation for 20 random sources to see if there was at least one zero, and ...
1answer
53 views

### Electric potential : numerical value for the triple Integral

The function $\phi:L\to\mathbb{R}$ where $L={\{(x,y)\in\mathbb{R}^2:x^2+y^2=4\}}$ is defined as, \begin{align*}&\phi(x,y)=\\ &\int_{0}^{\pi}\!\!\!\!\int_{0}^{2\pi}\!\!\!\!\int_{1}^{2}\!\!\frac{...
1answer
50 views

### Cauchy problem for an ordinary equation not in normal form

Let's consider a one-dimensional physical system ($x$ is the position and $t$ is time) described by a first order differential equation. I'm aware of the fact that if the equation can be put in normal ...
1answer
49 views

### RLC circuit differential equation

Question: Consider the RLC circuit shown in Figure, with $𝑅 = 110 \Omega, 𝐿 = 1 H, 𝐶 = 0.001 F$, and a battery supplying $𝐸_0 = 90 V$. Initially there is no current in the circuit and no charge on ...
1answer
55 views

2answers
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### Is there a proof that no rational number splits the octave equally?

In music circles, when the topic of tuning comes up, it is said that there is no rational number that splits the octave (the interval between a musical pitch and another with double its frequency, for ...