Questions on the analytic and numeric equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).
1
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1answer
74 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
1answer
80 views
Finding rational roots to an equation (univariate) [closed]
So I'm using Mathematica 7 for Students and I'm using the Root function to find the roots of an equation over the rational numbers:
$$225x^6 -343 = 0$$
I created ...
1
vote
1answer
103 views
How to extract Solve results as variables [duplicate]
Possible Duplicate:
Assign the results from a Solve to variable(s)
In the following example:
...
1
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1answer
99 views
How to find the values of $m$ so $A \cap B = \emptyset$ and $A \cup B = (-3,+\infty)$?
I have two intervals $A = (-3, m^2- 2]$ and $B=[m, +\infty)$. How to find the values of $m$ so that $A \cap B = \emptyset$ and $A \cup B = (-3,+\infty)$?
I tried
...
1
vote
1answer
131 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
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1answer
96 views
Finding parameters for first positive root of solution to differential equation to be equal to a desired value
I have a differential equation with parameters. The objective is to vary the parameters such that the first positive root of the solution is equal to a desired value ...
1
vote
1answer
78 views
How to get a solution involving logs in the right form?
How do I get
Solve[(1/9)^(r/2) == 1/n , r]
to give me
Log[n]/Log[3]
and not
...
1
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1answer
142 views
Remove failed Solve[] attempts
I can't figure how to replace a failed evaluation with a null value.
I am very new to Mathematica.
I have an equation that are being processed using the Solve[] ...
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1answer
164 views
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0answers
55 views
Bounds on random number
I have a Markov Chain Monte Carlo code that uses a chi squared function to fit some data.
I am running into an issue now with getting unrealistic values for some of the free parameters
in the code. ...
1
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0answers
82 views
I can't solve this set of equations
I am having trouble solving a set of equations in mathematica. I do not get any errors, but i don't get any answers as well.
I have some restrictions on my parameters and variables in the equations ...
1
vote
0answers
6 views
Identify the curve from the sample points [migrated]
I am writing a script which will identify the patterns drawn on the touch-pad of the laptop. I have generated all the points where user moved his finger over the touch-pad using synclient.
Now i ...
1
vote
0answers
49 views
Finding Maximum Root [duplicate]
How can I find the greatest root for a polynomial if the polynomial degree is very large.
One way is using NSolve. This command can find all roots in numeric. Then, ...
1
vote
0answers
72 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 ...
1
vote
0answers
70 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 ...
1
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0answers
121 views
NDSolve equations contain solution from solving cubic equations
I'm having trouble using NDSolve to solve equations that were obtained from solving cubic equations.
In my problem, I first obtained 6 functions (ca1, ...
1
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0answers
93 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 ...
1
vote
0answers
132 views
Does Solve give every solution?
When I run the following:
Solve[{
ac == anc, ac == acn, ac == ancn,
acn == anc, acn == ancn,
anc == ancn,
q1 + q2 + q3 + q4 == 1
}, {q1, q2, q3, q4}
]
I ...
1
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0answers
253 views
Calculating the mean curvature of a surface - suggestions
I am attempting to calculate the mean curvature [1, 2] of a surface defined by a function of x and y.
My function is rather ...
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0answers
77 views
Symbolic FindInstance
I'm wondering if there is any way of doing something like the following:
FindInstance[x < y, {x}, Reals] and getting, as a possible return value, ...
1
vote
0answers
89 views
Skip one step of the loop if there is NIntegrate::eincr: message
is there possibility to skip one step of the loop if in this step there appear error like NIntegrate::eincr:? For example: when I use "do" loop and when one of the step is evaluating I would like to ...
1
vote
0answers
274 views
Using constraints in Solve[]
I'm not sure if the title fits.
I'm basically just looking for a way to define a value and constrain it to $[a,b]$ when I use Solve later.
More specifically, I ...
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1answer
143 views
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1answer
338 views
How can I understand the result Mathematica returns from DSolve?
I have solved an ODE using DSolve, but I have a problem with understanding the solution.
In general the solution is in the form:
...
0
votes
1answer
142 views
Solving linear equation
I want to solve following linear equations:
\begin{align*}
3 x - y &= 0\\
y + 2 z &= -1\\
x + y + z &= 3
\end{align*}
The output will be ...
0
votes
1answer
145 views
FindRoot on a 2D list of Equations
I have a $n \times k$ Matrix of data that I want to feed into an equation and solve for an unknown variable. I suppose I can always just convert the Matrix into a long Array but I'd like to learn how ...
0
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2answers
130 views
Constraining two points, a specified distance apart, to a line
Suppose that I have two points in the xy plane: pt1 and pt2init. pt1 is fixed in space, ...
0
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2answers
148 views
Derivative of the solutions by parameter
P0 = 0.1;
K = 1000;
Quiet[sol = Solve[{K*P*L == PL, P0 == P + PL, r*P0 == L + PL}, {P, L,PL}][[1]]];
complex = PL /. sol;
Plot[complex, {r, 0.1, 2}]
How can I ...
0
votes
1answer
120 views
x/.NSolve[f==g,x] does not work when f or g is the output of NDSolve!
I have been trying to put Points at the intersection of two curves, one of which is the ouput of a differential equation solved with NDSolve. The output being an Interpolation, NSolve cannot find the ...
0
votes
1answer
96 views
Solving a system of equations using subscripted variables
I want to solve this equation:
X(i, j) + C*Y(i, j) = Z(i, j)
Where
...
0
votes
3answers
224 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 ...
0
votes
1answer
112 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
1answer
157 views
Solve telling me all my solutions are zero
I'm trying to use Mathematica to solve a complicated system of equations. Here is a screenshot of the equations, and what Mathematica outputs.
The variables $v_i$ and $w_i$ act as constants in ...
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1answer
122 views
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1answer
536 views
Solve matrix equation A*X=X*B using LeastSquares
I want to solve matrix equation A*X=X*B using LeastSquares method, but it is suited for equation like A*X=B.
All matrices are 3x3
...
0
votes
2answers
70 views
Reduce on equations involving integrals
Here's part of problem from a college physics text:
A time-dependent force F = (8.00 i - 4.00 t j) N (where t is in
seconds) is applied to a 2.00-kg object initially at rest. (a) At what
time ...
0
votes
1answer
227 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 ...
0
votes
1answer
99 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:
...
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2answers
94 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 $m$
...
0
votes
1answer
163 views
I can't get Compile to work
I've got some problems with my code, and I try to make it faster. Some of you suggested me to split my problem, and I'm here...
I post the same function with and without Compile.
This is a support ...
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1answer
112 views
Solve not satisfying simple boundary conditions
I am trying to solve the following equations for the coefficients c1 and c2.
...
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1answer
115 views
Industrial Level Applications. Recipe for mixed notation of equations set
I am working with large (linear) equations set within Mathematica in numerical notation. For example, set from 4056 eq. is solved for a second, no more. There is no doubt, result is great. But even ...
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1answer
495 views
Tricks for solving (lots of) coupled nonlinear equations numerically?
I have a system of 6 non-linear (quadratic) coupled equations with 6 complex unknowns
\begin{align*}
|x_1|^2 + |x_2|^2 + |x_3|^2 &= a\\
x_1 x_4^* + x_3 x_5^* &= b + c i\\
x_1 ...
0
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1answer
104 views
0
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1answer
88 views
Numerical rule evaluation -> {True, False} to deviation of target equation
I solve some equations numerically with FindRoot[] returning a quadruple {1,2,3,4}.
Because the solver sometimes do not find any roots depending on parameterization of these equations I select only ...
0
votes
1answer
48 views
Define variable relationships and dynamically update variables
I would like to define a relationship between 3 variables first and then later when I have filled two of the variables with a number, I would like to extract the value of the last value.
For example:
...
0
votes
1answer
36 views
How to delete duplicate solutions of this system of equations?
I want to find vertices (has integer coordinates) of the triangle $ABC$ with the centorid is $G(1,1)$ and orthocenter is $H(3,3)$. I tried
...
0
votes
1answer
187 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
114 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 ...
0
votes
1answer
104 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 ...
