Tagged Questions

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

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2D plot using output from the other function

I would like to get 2D plot using output from the other function. FindInstance[0.5*x^2 + Cos[y + P] == 1, {x, y}, Reals] By changing values of P manually it gives ...
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Potential flow over cylinder with FEM: Pressure field is flipped

Much in the fashion of a few problems already answered on Mathematica.SE (1, 2), I am trying to solve the Laplace equation in velocity potential $\phi$ to simulate irrotational, inviscid flow over a ...
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“Reduce” an expression in terms of a sub-expression

Newbie here. I've been trying to use Reduce to solve a rather long equation. The evaluation has been running for more than hour now, but still hasn't stopped. I've got an inkling that if I were to ...
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Mathematica - Count number of zeros of a function in an interval

Let's say I have a function, F[x_,d_] = Sqrt[(x^2 - 1)^2 + d^2], and I want to count how many roots (no root, or one root, or two roots etc.) it has in an ...
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Defining the domain of positive real numbers

I am trying to solve an equation by assuming that all the variables are real and strictly positive. I can use the keyword Reals for the argument ...
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Solving for flow speed?

I'd like to use Mathematica to verify the results of a Matlab code that iteratively solves for a flow velocity, u, given some fluid properties and a pressure drop. Ideally, I would like solve the ...
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Solving equation containing Erf expressions

Given the equation below, how do I find the value of b so that the function is equal to 21. I tried solve but I keep getting an error message. ...
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NSolve & PrecisionGoal

I am using NSolve to find numerical solutions of a particular equation. I do not need the solutions to as high of a precision as the other numbers in my notebook. To improve run time (I am iterating ...
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Computing Poincaré symbolic solution for an arbitrary integer order polynomial

In the 1880s, Poincaré created functions which give the solution to the nth order polynomial equation in finite form. These functions turned out to be "natural" generalizations of the elliptic ...
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Optimizing alphametrics code

First of all, thank you all in this great community. I have been reading a lot of threads about Mathematica optimization learning things like using Compile ...
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Seeking simple function in interval

I am a bit rusty, and struggling to solve this problem. Looking for a simple, well behaved parametric function f[t], from [0,1] to [0,1] such that: f[0] = f0; f[1] = f1; f'[1] = ff1; where -1<= ...
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Solve an equation for a product

I have an equation a = bcd/fg and I have another one that I can take bcd out of. Easy enough to do by hand, but Mathematica won'...
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Multiple dynamic equations for plotting?

Say I have a bunch of equations between variables e.g. h=bcd, i=hce, j=ihbd, ...
226 views

Solving Differential Algebraic Equations as BVP

I am trying to solve a set of DAEs. -4 \nu (\lambda(s))^{(-1 - 4 \nu)} \theta'(s) \lambda'(s) + (\lambda(s))^{(-4 \nu)} \theta''(s) = -\alpha_y \cos\theta(s) + \alpha_x \sin\theta(...
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Solving 4 variable system of equations

Trying to solve a systems of equations. Here's the code: ...
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How can I get Solve to combine Sin/Cos into Tan?

I want to solve an equation in x, containing Sin[x], Cos[x] and a positive real constant <...
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How to explain NDSolve that functions must be positive only?

I have a simple system of differential equations to solve but both functions should be positive: x[t] > 0 and y[t] > 0 for all t. I was not able to explain NDSolve this fact so it goes x[t] < 0 ...
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Find solutions of equation involving Bessel functions

I'm new in Mathematica and I'm trying to find the solutions of this equation involving Bessel functions $$\eta \frac{ J_{n+1}(\eta a)}{J_n(\eta a)}+\chi \frac{ I_{n+1}(\chi a)}{I_n(\chi a)}=0$$ ...
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Mathematica Solve function does not solve double exponential

I am trying to solve: Exp[-a Exp[-x/b] - c Exp[-x/d]] == Y to x, and using the command ...
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Simple differential equation to solve

Suppose we have this differential equation: $$x^2 + y^2 + z^2 = \frac{\frac{\partial y}{\partial x}}{x+y+z}$$ I want to find $\frac{\partial y}{\partial x}$ at x=1,y=1,z=1. I tried this code but ...
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Graphical solution of a a two-variable system containing an equation and an inequality

I'm currently studying atmospheric-gravity waves and their dispersion relations. I want to have look at values of $(x,y)$ that solve the following system : \label{}(1) \left\{ \...
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Quadratic Equations $\bmod p^k$

As part of a larger program, I need to solve $A x^2+B x+C \equiv 0 \pmod {p^k}$ for prime $p$. Right now I'm doing this by calling ...
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Resonance Curve using NDSolve

I am trying to make a resonance curve like this one below, using NDSolve. I tried to use code as below. Basically I try to hold solution for a w (driving frequency value) using NumericQ and then ...
I have got to solve a second order equation, where the coefficient depend on the parameter $k$: $$(A_k - \omega) (D_k- \omega) - B_kC_k = 0$$ so that also the solution $\omega=\omega(k)$ will depend ...