Questions on the use of numerical functions NIntegrate and NDSolve.

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1answer
117 views

Better way to check conservation in NDSolve

The partial differential equation in the NDSolve below is conservative (by construction) of $\int_{-1}^{+1} p(t,z)\ dz$ for all $t$. ...
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1answer
144 views

I integrate a real function, I want a real result [closed]

I want to count some integral in Mathematica (actually, check that this integral is zero...) I arrive to an answer which has a zero real part but has some imaginary part! Why? This could be a mistake ...
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1answer
131 views

Question with ParametricNDSolveValue

When solving the following system: ...
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2answers
200 views

Is there a better way to approximate some graphs of integrals than interpolation?

I'm still pretty new to Mathematica so my apologies if this is a dumb question. I wanted to plot some integrals of functions for no particularly good reason, but the only decent way I could come up ...
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1answer
150 views

Notation for numerical solutions to differential equations

Can somebody explain this notation to me? Using Mathematica's first example in the NDSolve documentation: ...
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2answers
518 views

NDSolve solution for driven damped pendulum diverges

I want to solve numerically for the system of the driven damped pendulum using Mathematica. This is the second-order nonlinear equation \begin{equation} \ddot{x} + 2 \beta \dot{x}+ \omega_0^2 \sin ...
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2answers
536 views

Why Can't Mathematica Integrate this?

I have the following problem from a textbook I am trying to integrate: So, following the directions in text, I am required to integrate each function. However, I cannot get Mathematica to integrate ...
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1answer
44 views

How can I perform this integration in Mathematica? [closed]

I am new to Mathematica. I want to find the integration of the following expression: $H(f)=T\left(\frac{sin(\pi f T)}{\pi f T}\right)^2$ Here, $T=1.127e-7$ I want to integrate this function for a ...
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1answer
48 views

Difference between NIntegrate and Integrate results

I want to integrate a function of two variables that is defined via a piecewise function. I can compute the integral analytically as follows: ...
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1answer
70 views

Numerical integration and plotting

New to Mathematica, and trying to numerically evaluate two integrals: ...
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1answer
52 views

Numerical integration of a three dimensional array

I need to integrate a scalar valued function $f\left(\boldsymbol{x}\right)$ where $\boldsymbol{x}$ is a three dimensional position vector; in other words: $\int_{\Omega} f\left(\boldsymbol{x}\right) ...
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1answer
48 views

nintegrate: greater accuracy possible

I've got the following piece of code: ...
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1answer
83 views

Mathematica answers `Solve[Integrate[f, x] == x^4, f]` wrong [closed]

The input Solve[Integrate[f, x] == x^4, f] ouputs {{f -> x^3}} Why?
0
votes
1answer
54 views

Different results for NIntegrate for the same function using cartesian and polar coordinates

This is probably a straightforward question. I have two functions f[x_,y_,z_] and g[r_, theta_, z_] where: g[r_, theta_, z_] returns f[ r Cos[theta], r Sin[theta], z]. For the same points in ...
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1answer
47 views

Error messages from NIntegrate [closed]

I've been trying to work on some integrals (Actuarial Science, for those interested) but somehow this always returns an error for me. ...
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2answers
86 views

NIntegrate Error

I am trying to solve this expression with the function NIntegrate: ...
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2answers
96 views

Numerical Integration

I have used the following code to evaluate an integral (val) numerically ...
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1answer
136 views

Plotting an function defined by an integral [closed]

How can I plot a function defined by an integral. More specific, I have the following equation: $$ T = ...
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2answers
138 views

Integral with unreliable result

I want to calculate $\int_R^1 \sqrt{r} |\cos((k+\frac{1}{2})\pi r)|dr $ and I get a result from Mathematica. Then I try to check the result putting the value of $k$ and $R$, (k=1 and R=0.5) in the ...
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1answer
71 views

Compute integral symbolically

I want to compute the following integral: ...
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1answer
167 views

Numerical solution of the hyperbolic equation

I am trying to solve the following hyperbolic equation with given boundary conditions: I choose as initial condition $u=1$, and evolve the above hyperbolic equation until reaching a stationary ...
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1answer
71 views

Numerical integration with purely numerical integrand

I'm trying to perform a numerical integral with an integrand that should not be manipulated with any symbolic preprocessing whatsoever. Consider the following simple test : ...
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1answer
43 views

Calculate Integral with cos [closed]

Integrate[ (Pi/4 - x/2) cos (n *x), {x, 0, Pi}] This doesnt give me desired results .n is natural 1,2,3,4,5... I want to get something like ...
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1answer
153 views

How to solve this integral equation?

I am trying to solve for x the integral equation : ...
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1answer
238 views

Infinite expression 1/0.^(1/4) encountered in NDSolve

I am trying to solve very simple system of coupled differential equations using the NDSolve function, but I am getting ...
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2answers
413 views

Double integral with variable in the limits

I'm trying to solve this integral: $$ ...
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1answer
409 views

How to use NIntegrate in a function using parameters from a list

I would like to use NIntegrate in a function with some parameters from a list. I simplified my problem for this forum. The list of parameters is as follows: ...
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2answers
220 views

NDSolve boundary query / Extracting values from solution

I have a function $O_{2}$ with boundary conditions $O_{2}(r_{o}) = p_{o} $ and $O_{2}(g) = O_{2}'(g) = 0$. I plot it using the solver code below; ...
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2answers
166 views

NIntegrate using Boole doesn't work

This doesn't want to work for me - I don't know why not. It usually gives me 0, but sometimes also a different number. I know it should be a small, non-zero number. ...
0
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1answer
530 views

NIntegrate & non-numerical values

I am wondering why I am receiving the message "The integrand ... has evaluated to non-numerical values for all sampling points in the region ..." for a particular calculation I am running. How can I ...
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1answer
1k views

Nested Nintegrate - two variable limits of integral

This is, so to say, the next part of the question: Nested NIntegrate - NIntegrate::inum: - error Now I define three functions: ...
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1answer
404 views

Nested NIntegrate problem

So I've been trying to evaluate the following integral in Mathematica 8.0 Student version: ...
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1answer
105 views

Time evolution of a wave packet from the time-independent Schroedinger equation [duplicate]

Starting off with the time-independent Schroedinger equation (TISE) $\quad \quad -\frac{\hbar^2}{2m} \nabla^2 \psi + V(r, \theta) \psi = E\, \psi,$ I would like to study the time evolution of an ...
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1answer
46 views

Adapt the code to produce a three column table containing the values of n, etc. (Numerical integration)

Here is a “procedural” program that we wrote in my class, implementing the rectangle rule of numerical integration: ...
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2answers
86 views

Multidimensional Numeric Integration

I can't manage to calculate numerically the following multidimensional integral: ...
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1answer
46 views

NdSolve problem :NDSolve::ndode: Input is not an ordinary differential equation

I am new to Mathematica. I am working on solving the following different equations numerically written in the code as below. Not so sure about the boundary values that depends on R (M(0)=0, n(1)=0) ...
0
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1answer
88 views

NIntegrate vs. summation

I' m interesting in distributions of points on sphere, plane figures etc. Especially for small number of points: 1, 3, 7, ... It seems that good criterion for uniformity of distribution is some ...
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1answer
65 views

Integration does not give real value

The code below must be obvious. We are trying to integrate a complicated function from 0 to 1. ...
0
votes
1answer
41 views

Problems using a complicated function within a LogLinearPlot [duplicate]

my problem is that I have a rather large function which I'm trying to plot, which looks something like this: ...
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2answers
85 views

NIntegrate and Integrate of a Spherical Bessel function

I am trying to integrate over a spherical bessel function. I have used both the Integrate and NIntegrate functions in Mathematica but the values given by each do not match. Any reason why this ...
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1answer
52 views

Integral for piecewise function inconsistent with the usual way

I have the following piecewise function: ...
0
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1answer
74 views

How to ensure efficient order of operations for rules, slots, substitutions?

I need to calculate several functionals Q[[t]] of a pdf f[x]. ...
0
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1answer
71 views

NIntegrate with units: unable to determine the units of quanitites that appear in the input

I want to integrate Planck's law of radiation in a certain wavelength intervall with units. I define some constants: ...
0
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1answer
93 views

NIntegrate:eincr error

I am trying to solve this expression in Mathematica with the function NIntegrate: ...
0
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1answer
59 views

Using ImplicitRegion to define an ellipse around Multinormal distribution for integration

I have both a 2D 'MultinormalDistribution', and also a single xy point, and I would like to be able to calculate the probability of this point (given the multinormal distribution) and also plot an ...
0
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1answer
722 views

wolfram mathematica intersection of two surfaces [duplicate]

I use wolfram mathematica. There is a function of two variables which defines the surface z = f(x,y), the second surface is defined as z = const. How to find the line of intersection of these two ...
0
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1answer
136 views

Help using NIntegrate

I need some help with NIntegrate. I pasted the code that I wrote below; I know that up to "de" is correct. What I would like to do is NIntegrate de w.r.t phi{0,0.1} and curlE{-10,10}. The final ...
0
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1answer
203 views

Numerical integration of two variable function

The aim is to calculate the definite integral of the function $f$ of the form $$f(x,t) \;\;\;\; x \in [0, \infty ) \;\;, \;\;t \in [t_0,T]$$ numerically. For example consider the function below $$f = ...