Questions on the analytic and numeric equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).

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3
votes
3answers
223 views

Simultaneous equations

I am trying to solve two simultaneous equations that are claimed to have 145 solutions but I believe they have 143, I want to check I am right before sending an email to my professor. Mathematica is ...
0
votes
1answer
62 views

Error when solving equations constructed with Table [duplicate]

I have a couple of questions about the problem I am trying to solve ...
1
vote
1answer
1k views

Green's Function in Mathematica

The equation I am trying to solve is: $$q \, T_1''(x)-T_1(x)(f-b \, g+i\,w \, p)=T(f_1-b \, g_1)-g_1\tag{1}$$ My professor says that $(1)$ can be solved by using Green's function $G(x,y)$, where ...
1
vote
3answers
1k views

Solve for variable in integral limit when using NIntegrate

I am trying to solve for a variable which appears in the limits of an integral, rather like in the following; ...
6
votes
4answers
488 views

FindInstance (and Solve, …) abysmally slow on a fully determined system of linear equations and inequalities: why?

I took a quick look for FindInstance and Solve-related questions but came up empty for the aspect that I am curious about. So ...
2
votes
1answer
122 views

NDSolve with different function lengths over time

I'm working on a cops & robbers game, and there is one single event that is very very important, the event of catching someone. I'm trying to do when any robber is catched, delete it from the ...
0
votes
1answer
66 views

How to ignore terms containing in the summation of multiplications

n=4;L=3; p0[n_Integer]:= Product[ Sum[Subscript[r, k][l, l], {l, L - 1}], {k, n}] // Expand; How to ignore terms containing three or more multiplications of [2, ...
0
votes
0answers
67 views

DSolve cannot solve for certain branches of the solution help pls

I get an error message while trying to compute this code.. help pls ...
0
votes
1answer
392 views

Symbolic matrix simplification and solving

I am trying to expand or solve an equation that contains matrices for a certain matrix, but it is not working: ...
12
votes
2answers
313 views

Behavior of Reduce with variables as domain

When using Reduce, I accidentally put a set of variables as the domain. To my surprise, it not only seems that Reduce expects ...
0
votes
1answer
186 views

Why is my PageRank result in Mathematica converging this way?

I am using this technique to find the PR of these 3 pages. It converges to something it shouldn't be. I tried the same iteration in Java and 2 pages come up with 1.333 and the other one as 0.666. ...
5
votes
2answers
222 views

How to “ReplaceAll” using a set of conditional expressions instead of a list of rules [closed]

Suppose that I have two linear functions f[x_] := f0 + f1 x g[x_] := g0 + g1 x and a (possibly rather complicated) set of conditional expressions, obtained ...
0
votes
2answers
48 views

Application on systems of equations [closed]

Lauren has 20 coins in her piggy bank, all dimes and quarters. The total amount of money is $3.05. How many of each coin does she have?
3
votes
1answer
374 views

Simulating a quick return mechanism

Last time, I got a satisfying answer for simulating a toggle mechanism, just as expected. NDSolve is great. I tried playing with it (as a matter of fact, @MichaelE2 ...
2
votes
2answers
238 views

Solving Inequalities with Gamma Function

I am wondering why Mathematica outputs that the following system "cannot be solved with the methods available to Reduce". $\frac{\Gamma(\frac{1}{2}+n)}{n-1}<\frac{\Gamma(\frac{1}{2}+k)}{k-1}$ ...
1
vote
1answer
243 views

Help to solve exponential equation over positive integers

I am trying to solve the equation $\frac{4}{9} = \big( \frac{1}{3} \big) ^n + \big( \frac{1}{3} \big) ^m $ with $n$ and $m$ both positive integers. I type into Mathematica the following In:= ...
0
votes
0answers
149 views

Solve system of non commutative operators

I'd like to use mathematica to solve systems of linear equations, where the entries are non commutative matrices. I just tried the NC package but it doesn't help so far. For example I can solve: ...
2
votes
1answer
109 views

FindRoot: Minimum Execution Time

Is there a minimum execution time for the command FindRoot? If so, can I get rid of it? For example, if I compute the time to solve the fundtion x=0, it takes around 0.27ms per evaluation: ...
0
votes
0answers
273 views

Solving coupled transcendental equations with Nsolve

I'm trying to solve a system of coupled nonlinear equations using NSolve: ...
1
vote
1answer
251 views

Mathematica Solve Hangs Indefinitely

The following code hangs ...
0
votes
1answer
72 views

Checking result for expression

I want to verify the following result: $\sum _{y=2}^{n+1} \left(\sum _{x=y-1}^n \frac{1}{x-y}\right)=n \left(H_n^{(1)}-1\right)$ In Mathematica i try with: ...
0
votes
2answers
110 views

Simplify an expression under certain condition

I have a variable A = g / (1 + g R) Actually, if the quantity (g R) >> 1 it is possible to write A as A ≈ 1/R. How can I do this in Mathematica? I tried with Assumptions, Refine, Simplify, but i can ...
10
votes
2answers
723 views

Finding all possible solutions to a math mind game

In the example below the letters shall be replaced by numbers. The numbers are from 1 to 9, and each letter has the same number ...
1
vote
0answers
58 views

Gram Schmidt Process for functions [duplicate]

I want to implement the Gram Schimdt procedure to the space of functions in the following form \begin{align}‎ ‎R(y,x)=\left\{‎ ‎\begin{array}{ll}‎ f(x,y), ‎& y\leq x\\ \\‎ g(x,y), ‎& y>x‎ ...
4
votes
2answers
157 views

Is there a giant AND symbol/How to solve tons of equations simultaneously

$$\sum_{k=1}^na_k=a_1+...+a_n$$ $$\prod_{k=1}^na_k=a_1\cdot...\cdot a_n$$ $$\large{?}\small{_{k=1}^na_k=a_1~\&\&...\&\& ~a_n}$$ What in mathematica would allow me to index logical ...
2
votes
4answers
806 views

Solving a polynomial equation with a condition of equality on roots

Let the following equation have two equal roots: f[x_] := x^3 - p x^2 + q x - r And I want to find out what the three roots are. Not knowing how to put this ...
14
votes
3answers
706 views

How can I simulate this toggle mechanism?

I've been introduced to Mathematica very recently. Basically, I haven't actually "solved" anything in my Mathematica lifetime, but I've done some simulations. With my fractional knowledge, I tried ...
3
votes
1answer
514 views

Methods for NSolve

I've been using NSolve a moderate (50-100 equations) size system of linear equations and it has been working splendidly (Solve ...
3
votes
2answers
323 views

Tweaking Solve for systems of polynomial equations

I am trying to solve the following system of $6$ quadratic equations in $6$ variables: ...
3
votes
1answer
187 views

How to solve an equation with two variables in Mathematica

If I solved an example equation like |x|+|y|=1 numerically, I would to get a 90° rotated rectangle. If I was to plot the equation, it would result in an image like ...
3
votes
1answer
80 views

Have transformation rules to be explicitly set?

I think this problem is not the hardest one, but I can't hit on it. I want to NSolve an equation. For this equation I use a transformation rule "ampTimes". First I used it like this: ...
0
votes
2answers
176 views

Eliminate variables by dividing two equations

how is it possible to divide two equations with Mathematica? I have the following code: ...
1
vote
1answer
373 views

Unable to solve a set of equations with Solve

I'm trying to solve the following equation using Mathematica 9.0.1.0 : ...
0
votes
1answer
286 views

How to write a variable in terms of the other [duplicate]

I have an equation that defines a variable like y=4x+a. I had another equation, z=x+2+4, I would like to know if there is a way in Mathematica to get an expression in which z= a*y+C, in which a and C ...
2
votes
1answer
158 views

Simplify equation using conditions/inequalities

If I have an equation like f[x](1 + a)==0 I'd like to be able to tell Mathematica that 1+a doesn't vanish in general, and get back ...
0
votes
3answers
126 views

Partial products in prime steps [duplicate]

I am trying to find out partial products going up in prime steps for Euler's product formula $$\prod_{p} \frac{1}{1-p^{-s}}$$ Trying things like ...
1
vote
2answers
223 views

Find the centre of FindGeometricTransform

I'm interested in using Solve[] to find the centre point of rotation (as an $x,y,z$ coordinate point) and axis of rotation (as a vector) from a ...
0
votes
1answer
76 views

Solving polynomial equations takes infinit time

I need to solve an polynimial equation, but when i try to use Solve or NSolve in mathematica, its cant find the solution in appropriate time (i interrupted calculation after 5 hour left). The ...
0
votes
3answers
189 views

Solving algebraic equations

How may I make n and k in terms of x and y in this ...
4
votes
2answers
189 views

Reduce with Integer domain, but receive a rational solution

I want to find the integer values $k$ so that D[f[x], x] has integer solutions. I tried ...
0
votes
1answer
196 views

Reduce Cannot Solve Complicated Function

As per the answer to this question: SolveAlways rejects inequality, I tried the following commands: ...
0
votes
1answer
123 views

SolveAlways rejects inequality

I have two functions of x, f and g. f[x] = g[x] + 2, ...
2
votes
2answers
192 views
1
vote
3answers
201 views

Plot a table of ranges

I have table with values like: t = {1.234 <= a <= 2.345, 3.42 <= a <= 5.67, ...} and I want to plot this table, the ...
3
votes
2answers
180 views

Solve-ing with initially unassigned parameters and Solve-ing using their numerical values produces different results

I am trying to solve an equation using the following piece of code: ...
1
vote
2answers
405 views

Equating coefficients in a non-power-series equation

How can I use Mathematica to equate coefficients in a non-power-series equation? For example, I would like to take an equation like the following: ...
2
votes
1answer
346 views

Speeding up solving a system of simultaneous equations

I am trying to solve the following system of equations. Solve takes a very long time to solve the following system of equations. Is there any way to speed it up? ...
2
votes
1answer
127 views

Declaration of variables in large Linear Programming model with NMaximize

I want to solve a large LP problem using NMaximize. This is a small instance of my bigger problem: $$max \sum^{4}_{t=1}(\sum^{4}_{c=1} V_{c}*f_{c,t})\\ s.t\quad ...
0
votes
1answer
93 views

Reduce[] giving incorrect result for equation over $\mathbb{Z}^4$

This is partially in response to a question I posted earlier, although the problem in this case appears to be distinct from the problem there, so I am temporarily filing this as a separate question. ...