# Tagged Questions

A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modelling.

46 views

### Choose which plants to build to maximise profit

What I tried: Let $y_i = 1$ if plant $i$ is to be constructed and $0$ otherwise Let $c_{ij}$ be transportation cost per-unit for whatever the plants produce delivered from plant $i$ to customer $j$....
92 views

### Maximise population coverage subject to budget constraint

Let $t_i =$ $1$ if transmitter i is to be constructed and $0$ otherwise, $c_j =$ $1$ if community j is covered and $0$ otherwise. Obj func: Max $$z = [10, 15, ..., 10] \cdot c$$ s.t. the ...
84 views

### What if the 'or' is exclusive instead of inclusive?

The context is an integer programming problem on choosing projects to maximise profit. I think (b) i. changes if 'either project 1 or project 3' means 'project 1 xor project 3' rather than 'project 1 ...
21 views

### Residual plot in the logarithmic model.

We've got some data containing two variables, where $x$ is the predictor and $y$ is the response variable. We make a model of the form of: $$y=\alpha+\beta \cdot x + \epsilon$$ Then we see that in the ...
51 views

### Population Growth problem using Malthusian Law and the Logistic Model

In 1980 the population of alligators on the Kennedy Space Center grounds was estimated to be $1500$. In 2006 the population had grown to an estimated $6000$. (A) Using the Malthusian Law for ...
22 views

### discrete population model, nondimensional

Re-formulate the following discrete population dynamic model in non-dimensional form: $x_{k+1}= r (1- \frac{x_k}{x_c}) x_k$ Notation in the lecture: $x_k$..size of population after k iterations, $x_c$....
87 views

### Linear Programming Mixed Assortment of Nuts

Below is a problem on Linear Programming. I think I have a start to it, but I'm in a rut right now so I was wondering if I could receive a little help. Here's the problem A candy store sells three ...
43 views

### Is this DE separable or homogeneous?

Differential Eq is $$\frac{(3y^2-t^2)}{y^5} \frac{dy}{dt} + \frac{t}{2y^4}=0$$ Is it linear in $y$ or $t$? Is it Bernoulli in $y$ or $t$?
22 views

### Symbol of equivalence between two functions except by constant

There is a symbol $\propto$ to show that two functions are proportionate to each other. Is there a symbol to show two functions differ by a constant? Say $f(x;y) = 2x + y$, I want something that is ...
37 views

### What is a good criteria for naming theorems/conjectures/lemmas?

Wikipedia, proofwiki, planetmath, and many others have various ways of naming theorems (and proofs and conjectures). I'm making a similar project, and am trying to create a searchable database of ...
20 views

### What is a Markovian time evolution model?

Supose I have to constuct a dynamical model for a random variable $X$ . Then I have read that for atmospheric and environmental purposes, a popular and flexible collection of models are (one-step) ...
25 views

### Transfer function of mathematical model

Im trying to derive a transfer function from by books end of the chapter exercise, but i can in no way match it with the given solution(given by our instructor). I was hoping if you can explain me ...
18 views

### Is $Φ^T$ a linear operator which transforms simultaneous equations such that we obtain LMS solution?

The below explanation is long winded, if you already know about using pseudo inverse to find the best fit solution to a set of simultaneous equations please go down to the tl;dr The Problem Given a ...
312 views

### Why is it important to find both solutions to a second order linear differential equation?

Given the equation $$y'' + y=0$$ A solution is $y=\sin(t)$ Why can't we stop there since we know a way to solve the system? Why should we consider all of the ways to solve the system? I would ...
23 views

### Differential equation modelling

I want to know where I have gone wrong. Please add a suitable title and tag.
25 views

### RINS: start - incumbent and relaxation solution have all different values

RINS: Relaxation induced neighborhood search; introduced by Danna et.al in 2010 this paper. I wanted to design an example how the RINS algorithm works to make sure that I have it completly understood ...
17 views

### NLP, Recatungular or Polar? Sine or No Sine?

Let's say we have the following complex number, $V$: $V=V_i+jV_j=V_m\angle{V_a}$ Which type of representation is better in an NLP (polar or rectangular)? The polar form leads to one nasty ...
55 views

### Newton's Law of Cooling and General advice on modeling with ODE

I have a question that goes as follows: For this question, assume that turkeys follow Newton’s law of cooling/heating. I start my oven heating at 12pm. The temperature of the oven increases linearly ...
33 views

### Book recommendation: Introduction to Traffic Flow and Traffic Models

I would like to look into the subject of traffic flow and traffic modelling. I have no prior experience with this, so it should be an introduction, preferably one with a level suited for a determined ...
69 views

### How to prove that the ellipse is a periodic orbit knowing that the orbital derivative of a function V is zero on there

The question is as follows: Show that the orbital derivative of the function $V=(1-x^2-2y^2)^2$ is zero on the ellipse $x^2+2y^2=1$, and explain why you can deduce that the ellipse is a periodic ...
62 views

### Fuzzy logic vs probability

In reading about fuzzy logic it says that fuzzy logic is different from probability. Can some one please explain how these two differ. How can this be explained to a person with no mathematical ...
17 views

### Warp shape and texture of the image into a common reference frame

I want to find object on the image using ASM and after that warp segmentation results into a common reference frame. So, I already have the algorithm of PDM and ASM and I able to find shape of object ...
36 views

### steady state or equilibrium

I need to find the equilibrium point of the following system of equation: $ds/dt = u - asi - bsw - us$ $di/dt = asi + bsw - (u + g)i$ $dw/dt = e(i - w)$ I found that $$s = \frac{u}{ai + bw + u}$$...
43 views

23 views

### On the computation of the Hessian matrix.

I'm trying to compute the Hessian matrix of a data fit of an ODE model to some data. Below is a cut out of the instructions I'm following (which can also be found at ...
133 views

### Why is “$\pi^2= g$” where $g$ is the gravitational constant?

Some months ago a professor of mine showed us a 'proof' of why $g\approx 9.8 ~\text{m}/\text{s}^2$ (the gravitational acceleration at the surface of the Earth) is 'equal' to $\pi^2\approx9.86\dots$ ...
53 views

### What would be a good cartesian equation to represent the shape of a wine glass?

I want to find the volume of a wine glass by using either the disk or shell method (solids of revolutions). The wine glass doesn't have to be of any particular dimensions, however it should roughly ...
67 views

### Bifurcation Diagram question for Population harvesting model $P' = rP (1-\frac{P}{K}) - hP$

A deer population grows logistically and is harvested at a rate proportional to its population size. The dynamics of population growth is modeled by $P' = rP (1-\frac{P}{K}) - hP$ where $r$ (the ...
56 views

### How can I calculate missing values from a table listing of areas and prices? [closed]

I have a set of objects of different sizes (measured in square metres). I know the price of some of them. I want to use the known prices to find the missing prices. Here is the data I have: \begin{...
22 views

### Where should I start from if I want to learn Mathematical Modeling?

I am a student of political science and have basic knowledge of mathematics. But I need to learn Mathematical Modeling if I want to continue a research of mine. I'm willing to spend even 1 or 2 years ...
57 views

### Construct differential equation given the phase portrait (non-linear pendulum)

I am curious to know how to recover the differential equation that goes with a phase portrait. I have seen the following posts but the first one was a $y'$ (and easy enough to "do in my head") and ...
40 views

### Can a statistical model have two unknown parameters?

Is an $N(\mu,\sigma^2)$ distribution a statistical model if both the parameters are unknown? The definition I have in front of me only refers to one unknown parameter.
36 views

### Is this partial differential equation solvable?

Ok so I am asked to set up a partial differential equation and then motivate why it is solvable. I'm only 2 weeks into my course so we are not asked to solve anything yet. However, if someone would ...
52 views

### can every object be represented mathematically?

I was just wondering if all 2D/3D objects/images/shapes could be represented by equations. For example, SpongeBob 2D curve and many more. How should I approach, as in, some theories that already exist?...
42 views

### Help with Differential equation solution requried

Hi guys I am doing some differential equations and I got this one: I have no idea how he went from (38) to (39). When I solve it by integrating factor, the equation I have is: c_{A}{(t)}=\frac{{c_{...
30 views

### A model for constant temperature of water in a container

I put some water in a container with initial temperature $T_0$ in a room, and the room's initial temperature is $T_a$. Now the container is filled to the maximum, so any more water coming in will ...
13 views

### Function representing learning review graph

I've been working on this for a while but am unable to get it right. (If anyone is curious, I'm trying to make a model that determines a user's best time to review something that he has studied, this ...
38 views

### Non-dimensionalization of a system, what to do if we have to divide by zero?

I have some PDE system involving unknowns $u$ and $v$ and $w$ which are concentrations of some substances. I want to nondimensionalize the system, so I divide through $u$ by some number $c_u$, and ...
22 views

### fidi of Chi-square Random Field

The $\chi^2$ random field $U(t)$ with $n$ degree of freedom (dof) is defined as: \begin{align} U(t) = \sum_{i=1}^n X_i(t)^2, t\in\mathbb{R}^N \end{align} where $X_1(t),...,X_n(t)$ are i.i.d ...
105 views

### Which distribution function for diseases

I am wondering, what would be a good method for choosing a suitable probability distribution to fit a certain criteria. For example, I am wanting to choose a suitable distribution, and specify the ...
20 views

### What is the difference between a first order compartment and diffusion

Biologists use Compartment models to represent the flow and storage of fluids in an animals body. In tissue (like muscle) the diffusion of blood is more accurately represented by the diffusion ...
104 views

### Equation for human body shape

I was wondering if anyone knows about or has created an equation that models a human body in 3D space. I imagine it would be based off of a cylinder or ellipse, but I don't know for sure. Note: I ...