Questions on the numerical functions of Mathematica, implementing numerical methods and numerical computing with Mathematica.
1
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1answer
149 views
Problem with Eventlocator Method for NDSolve
I want to solve the ode and plot the solution v[x] for different values of parameter a where ...
1
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1answer
98 views
What do these error messages mean when numerically solving differential equations?
I am using Mathematica to numercially solve the following equations:
...
1
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2answers
106 views
How do I prevent this precision exception?
I have the following as the first step to a sequence.
x = 2 - GoldenRatio;
Ceiling[x + x^(1/2)]
It gets a precision exception. The value is correct, but I would ...
1
vote
0answers
113 views
Adapting NDSolve to circumvent NDSolve::bdord: error for 1-D Euler Equations
I attempted to use NDSolve for the 1-D isentropic unsteady flow equations with low subsonic inflow velocity and prescribed inflow total enthalpy; along with a ...
1
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0answers
61 views
Using Root for numerical evaluation [closed]
In my expressions I have a lot of roots to calculate. For example:
Root[#1^3 + #1^2 + #1 &, 1]
Since most of them cannot be solved analytically, I would like ...
1
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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
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0answers
148 views
NDSolve error when solving a BVP
I'm trying to solve the following BVP with unknown parameters (p and phi) using NDSolve over the period {Pi, 2 Pi}:
...
1
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0answers
132 views
Parallel linear algebra with arbitrary precision
Is it possible to do parallel linear algebra with arbitrary precision within Mathematica (in a simple manner, as is done for the machine precision)?
0
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1answer
143 views
0
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1answer
190 views
Tabulating Numeric Approximation
I was wondering how to approximate or tabulate values for this numeric approximation: It is the following: The confusing part is how to implement the subscripts in mathematica.
$y_{i+1} = (t_i - ...
0
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1answer
67 views
0
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1answer
76 views
What is the correct way to use NIntegrate inside the FindMinimum function?
I'm having minor issues with the FindMinimum function when using NIntegrate inside. The functions work perfectly well but I get ...
0
votes
1answer
87 views
Alleviating a bottleneck involving a function call with symbolic derivatives
I have a bottleneck problem involving a function call with symbolic derivatives.
I don't have much experience with Mathematica (or any dynamic language) and I'm certain that the way I've set this up ...
0
votes
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 ...
0
votes
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
votes
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
120 views
DAE - varying initial conditions
I want to solve a DAE-system and I want to vary more than one initial conditions and to manipulate them. I looked here:
Putting NDSolve into ParametricPlot
But it does not work:
...
0
votes
1answer
82 views
Non solutions returned by NSolve. And why does it return both phi and Cos[phi]?
Similarly to this thread
NSolve gives additional solutions that don't satisfy the equations!
NSolve returns "spurious" solutions, even increasing the working precision
...
0
votes
1answer
171 views
How do I numerically solve a custom function?
Whenever I use functions like FindRoot or NDSolve, it sends x through the function and deals ...
0
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1answer
79 views
How to guess initial complex value for FindRoot
I have to solve a transcendental equation for a parameter, say $\beta$. Now, the $\beta$ has a range from $ik$ to $k$ where $i$ is the usual imaginary root $\sqrt{-1}$ and $k$ is a real number. ...
0
votes
1answer
79 views
How could we define a function recursively?
Let us first consider the constructon of the following simple iteration
...
0
votes
1answer
132 views
How to build a grid of integrand points and numerically integrate?
If I have some function I know numerically only, say f(x) and each point $x$ takes significant time to compute so I have them all stored in some file as f(1)=0.232423, f(1.1)=0.3243432,....Then is it ...
0
votes
1answer
396 views
how to solve an implicit integral equation? (iterate to a functional fixed point?) [closed]
I reduced a (special case) of my problem to the following code. Even though in this special case all related functions are analytical, DSolve is not the tool for this, though I am indeed looking for a ...
0
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0answers
60 views
0
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0answers
40 views
How to force evaluation/numerical result of a function? [closed]
I defined a function m[x] using
...
0
votes
0answers
61 views
FindMaximum inconsistency
The code below seems to work for n<11. But for n=11, and above, it outputs newa then just outputs "beep" sound.
WhyTheBeep says "The kernel Local has quit ...
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0answers
294 views
Jacobi eigenvalue and eigenvectors algorithm
Suppose we have a symmetric matrix with dimensions n x n. I need to find the eigenvalues and eigenvectors of this matrix using the Jacobi method. I wrote this code:
...
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0answers
84 views
Speeding up numerical computations
So, after seeing this and this post, I was thinking whether there were any general rules for speeding up numerical computations (not only NIntegrate or ...
0
votes
0answers
153 views
Rounding values [duplicate]
In Mathematica 8 when I enter 1 - 0.99 - 0.01 I get 8.67362*10^-18 instead of zero. How do I fix this problem?
I am getting ...
0
votes
0answers
147 views
Boundary Value Problem
I have to solve this boundary value problem:
$$\frac{\mathrm{d}e_{3x}}{\mathrm{d}l}=(M_0+F_{0z}x-F_{0x}z)e_{3z}$$
$$\frac{\mathrm{d}e_{3z}}{\mathrm{d}l}=-(M_0+F_{0z}x-F_{0x}z)e_{3x}$$
...
0
votes
0answers
83 views
FindRoot is only passing two variables
When I run the code:
q0 = FindRoot[findarea[ch, rh, ah, lineh, intersecth, q][[1 ;; 2]] == ah[[1 ;; 2]]*r3^2,
{q, q0}][[1, 2]];
...
0
votes
0answers
72 views
Applying individual values (e.g. from a list) to the gain variable of a common PID
I am currently implementing more things into my model of a common kitchen / manufacturing scale and came up with the idea to assign different values to the gain variables of the PID controlling the ...
-1
votes
1answer
126 views
Minimization problem using FindMinimum. Functional value “is not a real number”? [closed]
This question is a follow-up of another one I asked a few days ago. I followed the instructions given in the answer provided by the user that responded. I modified that answer to solve another ...
-1
votes
0answers
54 views
Why is NonlinearModelFit calling the model function with symbolic arguments?
I have a model to fit which is made of numerical functions and so it can give a value for any numerical value of the arguments, but creates an error when called with symbols. ...
-2
votes
1answer
149 views
Problem with solving a differential equation [closed]
I need to solve the following differential equation:
NDSolve[{R[r, t], R[r, 0] == r/1000}, R, {t, 0, 30}, {r, 1, 30}]
Where ...
