# Questions tagged [system-variables]

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### Identifying the parameter that flips the solution

I have solved a system of ODEs numerically. As the plot shows, the solution SolJx is positive for the parameters I have chosen. However, if you decrease (more ...
1 vote
103 views

### Plot of phase portrait of system of 4D non linear differential equations

While numerically solving ths system of differential equations: ...
72 views

### Plot phase portrait of a system of ODE

I have the following system of 4 differential equations: ...
21 views

### Replacing System definitions in a context whilst still maintaing acces to them [duplicate]

Given the system operator TensorContract I can define a new one, TensorContractLazy with the attribute ...
96 views

### Composition of functions not working [closed]

I am trying to set a function within a function. What I do is to first create a function with two arguments. Then I would like to set a new function with the same two arguments, in which the previous ...
63 views

1 vote
115 views

### How to obtain numerical solutions of a system of two equations with two unknowns?

I have two equations with two unknowns $-10<x<0$ and $0<y<15$ $$3 y \cosh (4 x) \cos (y)+(2 x+5) \cosh (x) \sin (y)=0,\\3 x \cosh (x) \cos (y)-(2 x+5) \sinh (x) \cos (y)=0$$ I would like ... 207 views

### Square root problem

Consider the following code NDSolveValue[{ x'[t] == x[t]^a, x == 0 }, x, {t, 0, 10}] which solves the equation $x'(t)=x(t)^a$, for some exponent $a$, with ...
1 vote
104 views

### Programmatically defining variables

I seems as though what I am interested in is unconventional, but I am interested in defining a number of different variables programmatically. For example I can write a matrix of variables by doing: <...
68 views

### Solving a multivariate polynomial system takes too long

I have tried to solve this system ...
37 views

### Is there a way to automatically store the output of a command to a variable directly?

Generally I do a computation then I have to manually take that number and make it equal to another variable which I define which I can then use to do subsequent computations. Something like this: <...
1 vote
260 views

### How to build a tri-diagonal matrix [closed]

I have an algorithm that works for a Tri-Diagonal matrix in Mathematica, but I need a good way to build my starter matrix A. It's a 20 variable system (and will be a 200 variable system once I get it)...
1 vote
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417 views

### variable K cannot be deleted

If a value is assigned to a variable that is named by capital K it cannot be deleted. This effect can be observed directly after start of the program. Is this a bug?
52 views

### What is the purpose of the two variables Globalargs and Globaldims [duplicate]

When opening the mma, I find that two variables Globalargs and Global`dims have been defined. One can check them by running <...
40 views

I am solving the following system of equations with Mathematica. $u'=-k_{1}ux+k_{2}x^2, x'=k_{1}ux-k_{2}x^2$ and I obtain the solution for x: $x(t)=\frac{e^{k_{1}C_{1}(t+C_{2})}k_{1}C_{1}}{-1+e^{k_{1}... 1 vote 0 answers 201 views ### NDSolve 2 functions 2 variables with intermediate calculation : (1 time-space eq) + (1 space eq) I have a system of differential equation with this structure :$$\left\{\begin{split}&\partial_t n(t,r) + \nabla. \big(n(t,r)v(t,r)\big)=0 \\ & f\Big(n(t,r),v(t,r),\partial_r n(t,r),\partial_r ... 0 votes 1 answer 94 views ### How to put equations in Block or Module to return n values? i have this code it return EigenValues, it's all right. Problem: i have to specify n in order for summation and solution to give output. Solution: i just need ... 5 votes 1 answer 246 views ### How to reset a built-in symbol to its default definition? I'm trying to add functionality to some of Mathematica's built-in functions in a package I'm building. I'm not trying to overwrite any functionality—just add it where it isn't already defined. I ... 0 votes 0 answers 143 views ### Minimize and Table of variables I use a list of variables to Minimize a particular quantity { Q, val1, Table[Pi, {i, 1, m, 1}} where i is the subscript of P. However in this way I have ... 2 votes 1 answer 285 views ### Solving equation with multi variable matrix input Background, here are the equations that I am trying to solve: Where R, E1, E2, V1, V2, P are all user inputs. X/A goes from -2 to 2 and Z/A goes from 0 to -2. Below is the code that I have so far. ... 0 votes 1 answer 69 views ### Choice of variables name affects the behavior of expression evaluation I tried to expand this polynomials. With x, it is increasing with the right order, however with b it is in a random order. The only difference is that I change b to x and it works. ... 12 votes 2 answers 619 views ### Catching MachineUnderflow in Version 11.3 Ilian's answer to question 72229, involves SetSystemOptions["CatchMachineUnderflow" -> False] Evidently, this worked in earlier versions of Mathematica, but ... 0 votes 1 answer 519 views ### How to permanently modify the$Path in Mathematica [duplicate]

I was trying to add permanently a path inside $Path. "/Users/Softwares/HEP_Softwares/MT-1.0" Following$Path manual I did the following ...
1 vote
308 views

### Solving a system of equations for a fraction

I want to solve a system of equations not for one specific variable but for a fraction of two variables. How can I do that? I want to solve: ...
263 views

412 views

### Interpretation of the result of ?@

This might be a very trivial question but as a beginner, I don't know the answer. I was exploring ? and after running a cell containing ...