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

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0
votes
3answers
462 views

How to find integer solutions?

Following is the equation: Need to solve for integer values of x,y when a,b lies between -1000 and 1000. Problem is to find the number of integer values of pair (x,y) that satisfy it.
2
votes
1answer
118 views

Deriving least-squares equations in Mathematica

I define $Y = a + b*x + e$, and I want to find values for $a,b,$ by least squares, so I minimize $RSS = sum((Y_i - a - b*x_i)^2)$ I then take derivatives, ${d RSS \over da} = 0$ and ${d RSS \over db} ...
1
vote
2answers
105 views

Symbolic solution of system

everyone! I am sorry, but I am an abcolute novice of Mathematica (to be more precise this is my first day of using it) and even after surfing the web and all documents I am not able to solve the ...
1
vote
4answers
252 views

How do I create a list of 25 random quadratic equations in the form ax^2+bx+c?

My teacher suggests using the RandomInteger command along with the Factor command, but I cannot figure out the syntax. A, b, and c need to be non zero integers between -10 and 10.
7
votes
1answer
226 views

How to substitute the following conditions into an expression?

I have an expression: $p=a\;b\; x + b^2\; y + a\;c\; z$. I want to substitute $a\;b=1$, $b^2 = 2$ and $a\;c = 4$ to obtain $p = x + 2y + 4z$. How can I tell Mathematica to do that? I dont know how to ...
0
votes
2answers
188 views

How to get a solution for the following equation?

When I try to solve this equation using Mathematica: Solve[Exp[b*x]-c*(x^2)-a*x-1 == 0, x] /. {a -> 6.336, b -> 8, c -> 32} I don't get any result and ...
0
votes
0answers
23 views

Jacobian matrix formation from polynomial expressions [duplicate]

I want to find the jacobian matrix for 3 polynomial expression with 3 variables.. the polynomial expressions have the degree of 8.how to form it.?
1
vote
1answer
106 views

Solve equations for all values of variables, rejecting certain types of solution

I have an expression, expr, containing 3 variables, 4 coefficients and 2 non-zero generic constants. I want to solve for the 4 coefficients such that the equation ...
6
votes
6answers
469 views

Can someone help me solve this x*y*z=180

I have one question I've been trying for a while but I can't get the result for my equation.. So I've been trying hard but I can calculate only by hand but the problem is that I am afraid to miss any ...
-1
votes
1answer
109 views

Solve set of non linear differential equations [closed]

I have set of differential equations. For example, I took two equations and tried to solve them as below. I am not getting any results. Please help me to figure it out the mistake. And I wonder if I ...
0
votes
0answers
48 views

Using Assumptions with Solve [duplicate]

Suppose i have a function defined as follows - f[x_] := E^-x - E^(-2 x); I want to find the max/min hence need to find when f'[x]==0. So i tried the following - ...
4
votes
3answers
237 views

How to find an approximate solution in a region when Solve or NSolve does not work?

Consider the relation x/Tan[Pi x] == y/Tan[Pi y] Solve or NSolve can't give a solution ...
3
votes
3answers
208 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
42 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
604 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 ...
0
votes
0answers
73 views

Finding a certain invariant polynomial using matrix coordinates

Here's a math problem that I would like to solve. This is also my first time posting on the Mathematica stackexchange website so please excuse me if this looks messy. Let ...
0
votes
2answers
68 views

Help needed with Simple equations [closed]

take a simple formula like Ohm's law u=i*r... is it possible to solve for i without values??, something like Solve[u=i*r, i] and expect an output like i=u/r which gives me: Solve::naqs: i r is not ...
1
vote
3answers
512 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
356 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
108 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
55 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
56 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
207 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: ...
7
votes
2answers
168 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 ...
-3
votes
2answers
105 views

Find the value by using FindRoot command [closed]

The equation x^4-3 x^3 = cos(3x)+3 has two real solutions on the interval from -10 to 10. Lets call these two solutions r and s. Use Mathematica's FindRoot command to find r and s. Now let M equal the ...
0
votes
1answer
160 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
184 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
41 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
273 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
189 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
138 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
55 views

Problem with equation solving using Solve

I understand that these kinds of questions may be a bit overdone but I can't for the life of me figure out what's wrong with this piece of code. ...
0
votes
0answers
115 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
92 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
191 views

Solving coupled transcendental equations with Nsolve

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

Mathematica Solve Hangs Indefinitely

The following code hangs ...
0
votes
1answer
68 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
102 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
542 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
57 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
143 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
379 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 ...
12
votes
3answers
543 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
344 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
274 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
140 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
68 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
148 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
232 views

Unable to solve a set of equations with Solve

I'm trying to solve the following equation using Mathematica 9.0.1.0 : ...