Tagged Questions

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

learn more… | top users | synonyms (4)

2
votes
2answers
251 views

A While Loop with two different steps/iteration

I'd like to know if there is a possibility to solve an equation in a while loop with 2 different steps. I want the step to be small at the beginning and bigger after a certain value of sigma (sigma is ...
4
votes
2answers
314 views

Extracting Reduce results

I'm solving a Diophantine equation inside of a function using Reduce but I'm having trouble extracting the necessary parts of the answer. For example, if my input ...
0
votes
1answer
783 views

Solving derivative of cumulative normal distribution log likelihood

I am a newbie and I'm trying to use Mathematica to obtain the symbolic Maximum Likelihood Estimation for a cumulative normal distribution. So far I have reached the step where I have the derivative of ...
2
votes
1answer
925 views

NDSolve two PDE plus one ODE, together

I have a couple of PDE (time and space/length) that are correctly managed by NDSolve, but to which I’m adding an ODE on which the acc “accumulates”, through time, a ...
2
votes
2answers
105 views

Puzzling behavior produced by Exists

I need to simplify a set of solutions of a system, say for example: ...
0
votes
1answer
1k views

DSolve fails to solve second order PDE

I have a very simple example of a second order PDE: eqn = D[u[x, y], x, y] + u[x, y] == 0; sol = DSolve[eqn, u, {x, y}] and Mathematica cannot solve it! What is ...
0
votes
1answer
218 views

Dynamic boundaries for FindRoot

As documented FindRoot[f[x], {x, xs, min, max}] searches for a solution, stopping the search if x ever gets outside the ...
3
votes
1answer
1k views

NDSolve does not respond

For some sets of constants, NDSolve gives me true solutions, but when I try for example, T = 1/(2*2200), Mathematica does not respond. What can I do? The code below ...
0
votes
1answer
169 views

Solving a differential equation for a variable in a function

This may sound like a very trivial question, but I need to solve a differential equation as follows: ...
1
vote
1answer
360 views

Substituting solution from Solve into the equation and making a plot

I want to solve an equation and substitute it into a Plot expression. My code looks something like this a[b_, x_] := bx + 1; sol = Solve[(1 + b)x + 1 == 0, b] I ...
11
votes
3answers
3k views

Solving a time-dependent Schroedinger equation

I want to solve the time-dependent Schroedinger equation: $$ i\partial_t \psi(t) = H(t)\psi(t) $$ for matrix, time-dependent $H(t)$ and vector $\psi$. What is an efficient way of doing this so ...
2
votes
1answer
133 views

Any solution to system of equations?

I need ANY combination of 8 variables which satisfy: a+b+c+d+e+f+g+h=0 a^2+b^2+c^2+d^2+e^2+f^2+g^2+h^2=1 a*b+b*c+c*d+d*e+e*f+f*g+g*h+a*h>2/3 Ideally these ...
7
votes
1answer
198 views

How to plot inequalities taking into account that points must be integers and not reals?

I have solved with Mathematica 9 the following integer inequalities using Reduce: ...
1
vote
1answer
212 views

Is my system too complicated for Solve?

I am trying to solve a system of three nonlinear equations using Mathematica. Solve takes forever to run and never solves my system of equations. Is my system too ...
1
vote
1answer
1k views

How to solve a simple inequality

I am having trouble getting Mathematica to solve really simple inequalities. I started with Solve[{y^x >= 2*y - 1}, x] but Mathematica can't solve it. So I ...
4
votes
3answers
676 views

How to solve this system of equations?

I want to solve the following system of equations: $$\begin{cases} 1+\sqrt{2 x+y+1}=4 (2 x+y)^2+\sqrt{6 x+3 y},\\ (x+1) \sqrt{2 x^2-x+4}+8 x^2+4 x y=4. \end{cases}$$ I tried ...
1
vote
1answer
129 views

Why Solve and Simplify give different results? [closed]

I want to solve the following equation y == (1/(1/4 + y) - 1/(3/4 - y))/((1/4 + y) + 1/(3/4 - y)) I tried ...
1
vote
3answers
2k views

How can I use assumptions with FindRoot?

I have something like FindRoot[f[x], {x, a}] Now I want FindRoot to constrain the solutions to 0 < x < 1. How can I ...
2
votes
0answers
146 views

Why is FindRoot initial value far from the specified one?

I am trying to numerically find the root of a function that looks a bit like: 1/x - (SchurDecomposition[A[x]][[2]])[[1]], where ...
7
votes
3answers
435 views

Efficient code for solve this equation

We have $a*b*c=-1$, $\frac{a^2}{c}+\frac{b}{c^2}=1$, $a^2 b+a c^2+b^2 c=t$ What's the value of $a^5 c+a b^5+b c^5$? I tried ...
2
votes
0answers
181 views

Solving $k\log(n) - k\log(k) \leq u$

How can I persuade Mathematica to help me find solutions to the inequality $k\ln(n) - k\ln(k) \leq u$ over the reals, assuming $u \geq n \geq k \geq 1$. When I evaluate ...
11
votes
1answer
238 views

FindInstance returns Indeterminate in version 9, but not in 8

Here is a trivial system of equations in three unknowns for which FindInstance obtains a solution: ...
2
votes
2answers
258 views
0
votes
1answer
92 views

Collecting roots of different equations and create a list

I solve two equations and have two solutions one by each equation. I want to create list of these roots. Could anyone please help me? Appreciate it. m02R150 = FindRoot[P1 == 0, {E1, 0.07, 0.1}] ...
1
vote
1answer
87 views

Calibrating Precision in calculations

As the title says, I encounter an irritating problem which has to do with the accuracy or the precision used in the calculations. To be more specific, I have the following code: ...
1
vote
1answer
376 views

Forcing evaluation of ArgMax

How to force evaluation of ArgMax before its output gets used in Solve? Background: I'm trying to solve for the Nash ...
0
votes
1answer
183 views

ContourPlot of a complicated function

I have the function $pot_1(x,y,z)$ which is given in analytical form. So, in order to plot the contours at the primary planes $(x,y)$, $(x,z)$ and $(y,z)$, I use the following ...
2
votes
1answer
318 views

Solving an equation involving a determinant

I have a matrix which doesn't include numerical values. There are four variables in it. It is defined by ...
-2
votes
1answer
1k views

Why can't Mathematica solve these non-linear equations? [closed]

$l_{2}$ and $\theta$ are the variables. All other parameters are constants. I need to find $l_{2}$ and $\theta$ in terms of these constants. $\frac{\mu_{0}\sin(\theta-\theta_{0})}{\sqrt{l_{2}^2 ...
1
vote
0answers
91 views

Solving for vector elements in a function to which the vectors are not passed explicitly

I want to define a function which takes in two integers (indicating the lengths of 2 vectors), and solves a simple set of expressions at a set of points to find all the values in both the vectors. so ...
4
votes
1answer
210 views

Can mathematica resolve this equation?

Obviously,the equation $x^2-3 y^2=2 z^2$ doesn't have positive integer solutions. I tried ...
3
votes
1answer
141 views

How can I get a single solution to a set of inequality constraints?

I have a set of constraints to which I require integer solutions. However, instead of needing all possible integer solutions (as obtained by using ...
3
votes
2answers
544 views

All possible solutions to the Matrix Equation (free variables appearing)

I am attempting to solve a system of linear equations using LinearSolve[] . In my case, the number of unknowns are more than constraints. I learnt that LinearSolve ...
1
vote
1answer
329 views

Stop Mathematica from giving imaginary solutions

I have the following equation: $$D=\frac{1}{64} \pi A ^3 B \sin \left(C\right)-\frac{1}{2} \pi A B \sin \left(C\right)$$ which I want to solve for $A$. The equation is cubic in $A$ so this should ...
1
vote
1answer
348 views

Solve equation with inequalities for parameters

I want to solve following equation: ...
2
votes
1answer
800 views

How to solve equations self-consistently

I want to solve the following equation self-consistently. So, H.u = e.u {{1, d}, {d, 1}}.{u1, u2} = e.{u1, u2} I guess an initial value for ...
0
votes
1answer
2k views

How can I get the solution of complicated implicit function?

The question is what is the method to solve the implicit function has real and imaginary number. For example, The function is $$F(x,y)=(-I*x + 2*y^2)^2 + x^2 - 4*y^4*Sqrt[1 - I*x/(y^2)]$$ Although ...
0
votes
1answer
209 views

Evaluating derivatives for use in solve

I need to evaluate the derivative of a function. My function looks like approx[vector_, x_] := Sum[vector[[n]]*Basis[n - 1, x], {n, 1, Length[vector]}] and I'm ...
4
votes
2answers
445 views

Finding all/most roots of a discontinuous function more consistently?

I have the equation: f[x_]:=α Tan[α*a] - Sqrt[c - α^2] and ideally I want to find all of its positive zeros, given a and c, with variable alpha. The problem is ...
2
votes
1answer
132 views

How to transform an expression using algebraical instead of pattern rules [duplicate]

I would like to transform rules algebraically. A very simple example would be: - k^2 - 2 k x + x^2 /. {2*k -> 1} This transforms to: - $$k^2-2 k x+x^2$$ ...
1
vote
0answers
217 views

Automatic inverse for Lambert’s Azimuthal Equal-Area Projection

I’m interested in finding closed-form inverses for map projection equations in general (of course, this is not always possible). I’m hoping Mathematica can help me with some of the trickier ones. As ...
3
votes
2answers
137 views

Find condition under which variables fall away

I have a somewhat lengthy expression, looking like expr = 1 + x + b + Pi + 2*a Is there some way of generating a relationship between ...
4
votes
2answers
504 views

How do I solve N simultaneous equations for N variables?

I have a function: f[x_] := x + 31 x^3 + 5 x^25 Which I want to find an expansion for: ...
8
votes
2answers
383 views

Finding all points of period n in an iterated map

I'm trying to implement an algorithm of Jenkinson and Pollicott to calculate the Hausdorff dimension of a Julia set for the map $f_c : z\mapsto z^2 + c$. It's described on page 40 of their paper, ...
3
votes
3answers
401 views

Symbolic derivative of $n$-term product

I want to determine the relationship that must exist between the $x_i$ and $y_i$ such that $$ \frac{\partial}{\partial\theta} \prod_{i=1}^n \frac{f(x_i,\theta)}{f(y_i,\theta)} = 0, $$ where $$ ...
8
votes
2answers
806 views

Find the parameter values satisfying conditions for all roots of an equation

Hi I'm very new at Mathematica. My real problems concerns a much more difficult equation with many parameters, but I want to check that the method is good, so I made up a test equation. My test ...
3
votes
1answer
226 views

What properties make this equation difficult to symbolically solve?

I tried to solve the following equation with Mathematica's solve: Solve[K*(2*Tan[L/2*Sqrt[P/(EI)]]-L*Sqrt[P/(EI)])+4*P*Sqrt[P/(EI)] == 0, P] It gave the ...
0
votes
1answer
233 views

Reap and Sow From NDSolve solution

I want to get the answer of my NDSolve in the form of table (the value of each x and y). ...
0
votes
2answers
140 views

How to get special solutions of this system of equations?

I only want to get all the solutions of this system of the solutions with a value of $k$, we have the same values ​​of $m$ ...
16
votes
1answer
691 views

Bug in Solve (Mathematica 9)

Just came across the strangest bug under both Mathematica 9.0.0 and 9.0.1. If one enters: Solve[m == p Sin[x] && -Pi/2 < x < Pi/2, x] ... then ...