Questions tagged [numerical-value]
Question relating numerical representations, operations and methods, including approximate results instead of exact symbolic results.
382
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Solving a Coupled System of Partial Differential Equations with Initial and Boundary Conditions
I am working to solve the provided system containing one PDE coupled with an ODE.
$G_t - \frac{\dot H}{H}\eta G_\eta -\frac{1}{H}FG_\eta +\frac{1}{H}F_\eta G + \frac{2FG}{\eta H}=\frac{1}{H^2R}[G_{\...
2
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1
answer
109
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How can I know for sure if I have a singularity or not when numerically plotting solutions to ODE's?
Here's my code for what I'm working on:
...
- 53
4
votes
1
answer
291
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How to port Matlab/Python's multivariate FoxH implementation in Mathematica?
Ref code
MATLAB
Python
My implementation
Are there some mistakes in my Mathematica code? Any help would be greatly appreciated.
Attempt Version 1 (❌)
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2
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1
answer
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Internal`MRealToString Gives Scientific Output From Large Inputs. How To Stop This?
The undocumented Internal`MRealToString works just fine for reals up to 999999. For anything over it outputs scientific notation. I don't need scientific, I need simple decimal.
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1
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0
answers
43
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TimeConstrained and optimization
I am trying to understand why wrapping TimeConstrained[] around optimization, e.g., MinValue[] can sometimes fail.
To reproduce ...
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1
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0
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60
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Help with a partial differential equation - inaccurate result
I'm trying to solve the following partial differential equation using NDSolve
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- 63
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1
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74
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How can I use the values of one plot in another one?
I have a two functions that I have to plot versus Q:
the first is Ri which is a solution for ...
- 15
2
votes
2
answers
222
views
Summation not returning a timely result
Why is Mathematica v12 spinning on this series:
FullSimplify[Sum[16^x/((16^x) + 4), {x, 1/2025, 2024/2025, 1/2025}]]
The answer works out to 1012.
Is there another ...
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2
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132
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Solution of an implicit integral equation
The present question is pretty similar to this one.
Here I want to find the solution of the following implicit integral equation:
$$
P_H(u)=\int_{-\infty}^\infty dJ \int_{-\infty}^\infty du_1 \int_{-\...
- 405
2
votes
2
answers
217
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Numerical derivative of numerical function
I am trying to calculate the derivative of a numerically defined Hamiltonian. This is a minimal working example (on a simple example):
...
- 133
1
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1
answer
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Errors in `NIntegrate` - or in coding?
As far as I know, if a set of functions f,g,h,... are all Riemann integrable then the definite integral of the sum f+g+h over ...
- 2,335
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0
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64
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A problem with obtaining the beam frequencies and mode shapes
I am supposed to find the mode shapes of two assembled beams. To this end, we must reduce the PDE equation of motion of beam to an ODE including the oscillation frequency. The solution of ODE has some ...
0
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0
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67
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NDSolve::litarg error and overdetermined system error in NDSolve
Before the long description about my problem, my question is How can I avoid NDSolve::litarg error and overdetermined system error in a NDSolve for simultaneous differential equation.
Nowadays I ...
1
vote
0
answers
74
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Problems with implementation of subresultant pseudo-remainder sequence in Sturm's theorem
I've implemented the subresultant pseudo-remainder sequences ( https://en.wikipedia.org/wiki/Polynomial_greatest_common_divisor#Pseudo-remainder_sequences ) as described in Wikipedia. However, when ...
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1
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NSum with variable sitting inside
I want to evaluate the following and many other similar expressions numerically from k=2 to k=Infinity with a variable ...
- 411
1
vote
1
answer
103
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Solving a 3+1D Wave Equation
I am having some problems with finding the solution to the magnetic field, B[x,y,z,t]. Is there anything I can change to my code to obtain a solution of B[x,y,z,t] with the initial conditions and ...
- 13
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0
answers
43
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How to find optimal solution
I want to ask something. Right now, I want to try to find the optimal solution from a function in a paper. here is the function :
And here is the numerical example :
There is solution procedure that ...
3
votes
2
answers
41
views
Strange behavior of MinimalBy [duplicate]
data = {{1, 2}, {2, 2}, {3, 3}};
MinimalBy[data, Norm@# &]
Output: {{2, 2}}
When applying numerically :
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- 1,894
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0
answers
56
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Interpreter fails to obey significant figure specifications
Consider the following example, where we specify the precision of the numbers to perform a significant figures calculation:
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- 3,388
2
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1
answer
108
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Finding roots for an expression with non-elementary function
Is there an approach to solving this for $a$ in either closed-form or numerically?
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- 3,410
0
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1
answer
68
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How to use multiple output from Nsolve? [closed]
I have 3 simultaneous equations and 3 unknowns. The values are coming to be right. But how do I assign these 3 values in the respective variables?
...
0
votes
2
answers
150
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How to numerically find complex non-real roots of a function?
Using Mathematica, how can we numerically find only complexes, but not real roots, of a function?
For example, if we have f:C->C, and we have roots like, R1,R2,...,Rn (real roots, without imaginary ...
- 1,536
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0
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How to Parse Binary .STL File Created on Ancient 32-bit Architecture
Import[fileName,"STL"] returns $Failed
The file format is so simple that one can calculate the number of triangles in the file
by counting the number of BinaryReads to reach EndOfFile.
https:...
1
vote
1
answer
116
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Can't solve equation numerically (Solution in terms of Root) [duplicate]
I am trying to solve the following equation numerically.
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2
votes
1
answer
132
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Solving a ODE (Peeble's Equation) with initial condition a the maximum input range
I have a differential equation which is,
$$
\frac{d X_e}{dz} = \frac{C_r(z)}{H(z)}\times \frac{1}{(1+z)}\Big[\frac{38\eta T^3}{25\pi^2}\alpha (T)X_e^2 - b(T)(1 - X_e) \Big]
$$
Where
$$
\alpha(T) = \...
- 174
1
vote
1
answer
64
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Is a four-variable function less than one?
I have the following function of four variables
f=Sqrt[(1 + w - x + 4 y z) - Sqrt[4 (-w + x) + (1 + w - x + 4 y z)^2]]/Sqrt[2]
I want to show that $f(w,x,y,z)<1$...
3
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0
answers
64
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Derivative[0, 1, 1][QPolyGamma] cannot be calculated numerically?
During a more complicated calculation, I got an expression
...
- 3,169
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2
answers
110
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Why can't NSolve find values that FindInstance can?
I am trying to solve for \[Epsilon], given three input paramters n, x and ...
- 496
5
votes
1
answer
187
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Why is Around omitted when the uncertainty is zero?
I have a list of values with errors and I use Around[x, dx]. Some of those values have an error of zero though. Mathematica removes the ...
- 53
0
votes
0
answers
68
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NSolve can't solve a system of 2 equations with 2 unknowns
I've been trying to solve a system of 2 equations with 2 unknowns using NSolve. But It's been too slow. I waited for more then an hour without any results.
The code is:
...
- 101
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votes
0
answers
40
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How to treat small numbers in order to gain efficiency and precision in neural network algorithm?
Unfortunately I won't be able to provide a MWE, as it would be too big and complex, and this question will be based on pure semantics, basically (and I understand if this is impossible to answer in ...
- 405
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votes
1
answer
128
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NMinimize can not find points that satisfy constraints
NMinimize cant find solutions for a function which clearly has one. Setting a working precision resulted in some output, however with error messages about tolerance and precision.
Heres my code. The ...
- 496
1
vote
0
answers
66
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Numerical Error using compile
I'm trying to compile a function and I'm running into the following error
CompiledFunction::cfne : Numerical error encountered; proceeding with uncompiled evaluation.
I think I have succeeded in ...
- 496
0
votes
1
answer
121
views
Performance improvements using Table and Compile
I'm converting a code from MatLab to Mathematica. It takes MatLab less than a second to compute it while its more than ten minutes in Mathematica. I was hoping to improve the performance.
Here's a ...
- 496
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votes
1
answer
69
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How to make faster of a code containing more iteration point? [closed]
I am trying to evaluate a code of the Power Series Solution method to get the results. Also, the time of evaluation depends on the parameters I am using. When the iteration point is 50, 60, or 80, it ...
1
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2
answers
169
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How to make faster of a code containing more iteration points?
I am trying to evaluate a code of the Power Series Solution method to get the results. Also, the time of evaluation depends on the parameters I am using. When the iteration point is 50, 60, or 80, it ...
0
votes
1
answer
120
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How to minimize numerical error in the code while solving the system of ODEs
I just want to ask in the graph of the code mentioned in the link, while plotting u from {-0.0001,y,0.0001}, the jump is coming because of the numerical error u1-u2. Can anyone please tell me, how to ...
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vote
2
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Finding closed form representations of floating point numbers?
Is there a trick to automatically recognize that ${-0.5771,1.2280}$ are approximately equal to {-EulerGamma, Log[2 + Sqrt[2]]}?
These were obtained by using ...
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0
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1
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54
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Proceeding integral or summation calculation with no explicitly designated quantities, but instead with an abstract 'n' quantities
Could someone kindly tell me how to calculate formulas such as integral or summation with no explicitly designated algebra quantities as derivatives or summands, but the abstract ' n' quantities ...
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0
answers
43
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Nested NIntegrate with Matrix Exponential
I wish to perform a numerical integration which involves a matrix exponential. Here's the following code
...
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1
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1
answer
82
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a problem in numerical integration in Mathematica
I am trying to numerically compute an integral of the following type in Mathematica. I can show that this integral can be computed analytically. Still, I want to make sure Mathematica can also give me ...
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0
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54
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Increase computation speed for nested integral equations
I want to numerically solve these two nested integral equations
$$q(J_0,T)=\int_{-\infty}^{\infty} \frac{1}{\sqrt{2\pi}}e^{-\frac{z^2}{2}}\,\mbox{tanh}^2\left(\frac{z\sqrt{q(J_0,T)}+J_0 m(J_0,T)}{T}\...
- 405
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0
answers
47
views
Identifying the parameter that flips the solution
I have solved a system of ODEs numerically. As the plot shows, the solution SolJx is positive for the parameters I have chosen. However, if you decrease (more ...
- 479
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0
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91
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Error in numerical integration using Wolfram Mathematica
I hope you are doing well.
I am having serious problems while calculating a numerical integral in Wolfram Mathematica, as the following error messages appear:
1- "Numerical integration converging ...
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0
answers
79
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Numerical solution system of ODEs
I want to solve the following system of ODEs with four boundary conditions:
...
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1
answer
209
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How to numerically solve differential equations with singularities?
I wish to solve a differential equation numerically. As an example, I tried solving Hypergeometric differential equation
...
- 307
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1
answer
60
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Value given by NIntegrate is double of Integrate function
I am performing a calculation where the result of NIntegrate and Integrate is different. They differ by factor of 2. Can someone tell what is the reason and how to make the NIntegrate value right?,
<...
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2
votes
2
answers
239
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Solving complex equation numerically
I'm trying to solve the following equation for $z$ for a set of given complex values of $a$ and for fixed $b$ (without providing any initial guess value(s)):
$2^{iz}~\Gamma\left(\dfrac{iz+b}{2}+1\...
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votes
2
answers
387
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How can I speed up calculation of the integral?
Is it possible to speed up the calculation of the Kx integral?
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- 1,883
3
votes
1
answer
87
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Why two the same integrals give different values?
Why two the same integrals give different values?
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- 1,883