Questions tagged [numerical-value]

Question relating numerical representations, operations and methods, including approximate results instead of exact symbolic results.

Filter by
Sorted by
Tagged with
0
votes
2answers
120 views

Why does mathematica not recognize the equality of these two terms? [closed]

I have two expressions which I have analytically verified to be equivalent but when I check them numerically via mathematica I don't obtain numerical agreement. They are ...
8
votes
2answers
340 views

how to get single, and quad Precision out of Mathematica which match Fortran result

by default, if a number has decimal . after it, then Mathematica will do computation using machine Precision, which on my PC (intel hardware) running windows 7 64 ...
0
votes
2answers
82 views

Numerical Function

I want to animate a Point moving on an ellipse, but the angle I need to use is a numerical solution from an epression. How can I get mathematica to just take the value from the animated nummerical ...
1
vote
1answer
53 views

TrigExpand for numerical multiples of angles

After some calculations, Mathematica gives me a result which has in it a term Cos[2.x] (I cannot skip numerical computing, that's the reason for the ...
0
votes
0answers
43 views

Error caused by ThreeJSymbol

I do not understand what causes non-physical answer in my code although I have read about the error. I am also getting the following error, how could I fix the example error: "CompiledFunction::cfte:...
0
votes
1answer
45 views

Numerical Results with replacement rules [duplicate]

Why are the following outputs different? N[(x^2 + y^2) /. Thread[{x, y} -> {1., 1.}], 10] gives 2.. N[(1^2 + 1^2), 10] ...
1
vote
1answer
123 views

Get Finer Grid with respect to x using NDSolve in Mathematica

I use Mathematica NDSolve to numerically solve V(x,t) and export the numerical values of V(x,t) at each x and t into an external csv file. I find Mathematica only numerically give results with step ...
5
votes
0answers
337 views

How does NSolve find the roots to an equation?

I'm using NSolve to find the roots to a transcendental equation. For this, I need to specify a bounded region where roots are searched. What I want to know is how <...
1
vote
1answer
68 views

Optimising matrix calculation [closed]

I was calculating the elements of a matrix like this: ...
18
votes
2answers
814 views

Error and uncertainty propagation: Is using Precision/Accuracy a sound strategy?

Questions What are the available resources to deal with experimental error and uncertainty propagation in Mathematica? Given that Mathematica already uses linearized model of error propagation on ...
2
votes
1answer
207 views

Orthogonalize with a custom inner product

Bug introduced in 9.0 or earlier and fixed in 10.0 I was trying to define a custom inner product function for Orthogonalize, and have been getting some odd behaviour. Here's a MWE: I try to compute ...
0
votes
0answers
62 views

Evaluating expression with machine arithmetic gives wrong answer but evaluating with arbitrary precision works

I need to understand how Mathematica approximates symbolic numbers. I have an awful symbolic number to compute. When I do N[variable] Mathematica gives me <...
0
votes
0answers
160 views

Limit of a List

Is it possible to take the limit of a list instead of using the Limit method? I'll try to explain what I mean. I am generating a list of numbers that converge to some number. The generated numbers ...
1
vote
0answers
82 views

Why the data from Do-command disagree with the plot I get using them? [closed]

This is a question relevant to How to plot output data of Do-command? The Differential Equation at hand now is $\frac{d^2 f}{dx^2} + \frac{2}{x+0.1} \frac{df}{dx} = k(f)$ I give the code with the ...
5
votes
3answers
242 views

How to plot output data of Do-command?

The following in a simple numerical solution of the simple harmonic oscillator. ...
0
votes
0answers
126 views

Problem with FindRoot + NDSolve + InterpolatingFunctionDomain

I'm trying to find the root (po) of a complicated problem (where s is a parameter): First, I need to define some functions, which involve numerically solving a differential equation. ...
1
vote
4answers
285 views

How to solve the following set of equations to find values of a1, a2, and a3

i am new to Mathematica, Can some one kind enough to show me how to solve the following set of nonlinear equations to find a1, a2, and a3.. ...
1
vote
0answers
40 views

Numerical evaluation after Normal? [closed]

I'm interested in numerical evaluation thru substitution: a /. a -> 1 (*=> 1 *) However if I used Normal in the "pipe" —...
3
votes
2answers
256 views

How can one generate an open-ended sequence of low-discrepancy points in 3D?

I'd like a low-discrepancy sequence of points over a 3D-hypercube $[-1,1]^3$, but don't want to have to commit to a fixed number $n$ of points beforehand, that is just see how the numerical ...
0
votes
1answer
102 views

Numerical value of an expression with a uniform step size [closed]

I have a complex expression that is so difficult to separate its Real part from it Imaginary part. What I thought of doing is to get the numerical value of the Real and Imaginary part, Then I will use ...
0
votes
1answer
463 views

Specifying precision of a number in StringForm[]

I want to use StringForm to provide the headers to a table of numbers I have just calculated. Basically, I want the top row of spots in the table to have the form $D = x~~\text{(nm)}$, where x ...
3
votes
2answers
286 views

Visualizing the Schrödinger equation for dipole based interaction Hamiltonian

I want to evaluate and plot the solutions of coupled linear differential equations. For each time frame, I want to display the probability values (corresponding to mod square of these solutions), and ...
0
votes
2answers
237 views

Numerical Differentiation of a Numerical Integral

I am trying to evaluate the following expression numerically $$\frac{d^2}{dt^2}e^{-2t^2}\int_0^\infty\frac{\xi/\sqrt{2}}{\xi^{3/2}}e^{(-\xi^2/2-2\xi t))}$$ My code is as follows ...
5
votes
1answer
104 views

N[Product] and NProduct give different results

I have some trouble. I've been using finite product to study a certain function (see below). However, when I wanted to compute it precisely, I decided to use ...
0
votes
1answer
110 views

How to fix step size in do loop? [duplicate]

I apply the following command: Do[Print[var[u] = u], {u, -1, 1, 0.1}] It produces out put. But when i recall the value var[-0.4] as below: ...
5
votes
3answers
322 views

How to complete function which is not defined for all interval

I have a function testF22 like this ...
0
votes
1answer
228 views

Solving a complex equation

I try to solve a complicated equation. To do that, I write (excuse me, I could not copy paste in an appropriate way from the notebook) ; ...
1
vote
1answer
129 views

Numeric calculation with many digits

I try to calculate something like 1.569732312*Pi and by default mathematica returns something like 4.93146 (only 5 digits after floating point), but I believe there is much more digits, especially ...
4
votes
1answer
115 views

Why does this test yield True

I have this test implemented in my code, when I import a numeric matrix, which I thought would be bulletproof, but it's failing in this case: ...
1
vote
0answers
82 views

Plotting the Full width at half maximum as a function of a parameter

I have this function and I want to plot the FWHM of it as a function of the parameter "a", defined between 0 and 10. It should look like the picture attached. I also put the original equation in case ...
3
votes
2answers
593 views

Plot numerical solutions for a varying parameter

I would like to solve this equation $\log{\frac{a}{1 - a}} + b (1 - 2 a) = 0$ letting varying the parameter $b$ in $\lbrace 0,1,\ldots,20\rbrace$ and then plot the result. I am trying writing the ...
1
vote
1answer
79 views

Getting non-real answers when assuming variable is real when trying to numerically find maximum entropy distribution

I'm trying to find the maximum entropy distribution as such: Assuming[Element[l, Reals], NSolve[Sum[Exp[l i] i/Sum[Exp[l j], {j, 0, 100}], {i, 0, 100}] == 50,l]] ...
8
votes
5answers
2k views

Numerical voodoo in mathematica? [closed]

So, I was doing some calculations in Mathematica, and came across the following paradox! (I may be exaggerating, but...) I wanted to solve the following equation: $3.33333*10^{-15} - 3.33333*10^{-15} ...
1
vote
1answer
190 views

NSolve/Reduce Help: 3Equations/5Variables

I have this system of equations that I have been trying to solve using Mathematica; I had been running this last evaluation for 30 hours and my computer crashed :/! So, instead of deciding to run ...
1
vote
2answers
54 views

Chains of approximate numeric equalities

Mathematica considers two numbers equal if "at most their last seven binary digits" differ. For example: ...
4
votes
1answer
594 views

What does it mean that “there are no significant digits to display”? [closed]

So I substitued with the following values in my function T(x,n) and it gave me this red box with the value in the picture. When I hover over it, it tells me that there are no significant digits to ...
2
votes
1answer
66 views

What Heads do not have the attribute NumericFunction, but still give True in NumericQ?

The following expressions give True in the NumericQ test: ...
1
vote
1answer
107 views

Can't get a numerical value for this vector operation

I have written these codes: ...
1
vote
0answers
60 views

Why doesn't N[0.33333, 3] return 0.333? [duplicate]

Basic question, other answers I found didn't really seem to address this. N[x,3] seems to only work if x is analytic instead of ...
0
votes
2answers
137 views

I'm trying to solve a system of complex equations

I'm simply trying to solve a system of equations and mathematica can't do it for all values over the region of interest. I have a 3x3 matrix that has a specific parametrization and after squaring the ...
3
votes
3answers
219 views

How to change random values in manipulate?

I made a Manipulate box that is working very well, using lots of random numbers. I would like to add a button to "reset" (i.e. to change, randomize, or reselect) all the random parameters. Here's ...
10
votes
3answers
844 views

What is the fastest way to compute digits of $\pi$ using Mathematica?

There are a lot of ways to calculate digits of $\pi$ using Mathematica. The most naïve way I can think of is N[π, 100000000] Of course, there are a lot of fast ...
3
votes
2answers
129 views

Role of Accuracy in numerical evaluations, SplitBy vs GatherBy

This is a follow-up question to this question. I generated a list by substituting the results of a solve[] routine and set: ...
4
votes
1answer
544 views

Recognize physical constants?

Is there some way to ask Mathematica to recognize physical constants, such as 32 or 9.81 (gravitational acceleration, in different units, at Earth's surface)? I have in mind something like the "...
1
vote
0answers
104 views

Using Classifier with NearestNeighbors methods

I am using a Machine learning toolbox on mathematica. I have 8 classes. Training data: for each class, there 100 samples with size 160. I used this code. ...
0
votes
0answers
91 views

Maintaining working precision in my program

I am badly stuck with this program I am writing. I want output of program below to be precise up to 25 digits after decimal point. I am supplying all inputs with precision 25. But after each iteration ...
0
votes
1answer
96 views

How to calculate digits of Trott Constants?

How to calculate digits of numbers (Trott Constant) whose continued fraction representation is the same as the digits of its radix representation with Mathematica?
34
votes
2answers
736 views

GroupBy twice gives different results

Bug introduced in 7.0 or earlier and persisting through 11.1 It took me quite a lot of time to finally trace down to this strange output. I really don't know why. First, I create a list ...
4
votes
2answers
212 views

Torus-geometry algebraic equations using NSolve and Reduce

Somehow a set of naive-looking equations cannot be solved by using NSolve. Mathematica returns a message like this: ...
1
vote
1answer
589 views

How to find and express all polynomial roots with greatest precision?

I've already plowed through the documentation and a bunch of other Questions on this, but I've only found partial or tangentially related answers. I need numerical results for all of the complex ...