Questions on the use of numerical functions NIntegrate and NDSolve.

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1answer
52 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
35 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
111 views

How to solve this integral equation?

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

Mathematica Compute Time Is Extremely Long (Integrate simple function with parameter scan)

I was wondering if you can help. I have a set of equations I need to solve for a list of parameters; entering each parameter value and solving anew each time is simply not economical. I found a way ...
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1answer
118 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
142 views

Double integral with variable in the limits

I'm trying to solve this integral: $$ ...
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2answers
122 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
426 views

Kramers Kronig Relation for Phase and Complex Reflectivity

I am a new user to Mathematica and I have been trying to figure out how to find $\Theta(\omega)$ from my 'experimental' values of energy and $\ln(\sqrt{R(\omega)})$ (I am just running a simulation, ...
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2answers
125 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
262 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
687 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
305 views

Nested NIntegrate problem

So I've been trying to evaluate the following integral in Mathematica 8.0 Student version: ...
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2answers
447 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
349 views

singularity in NDSolve and Table command [closed]

We are considering the following equations ...
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1answer
54 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 ...
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1answer
55 views

Integrating function can't be epressed? [closed]

Hi I have a function in a form of $$\frac{a}{x}exp(\frac{b}{\sqrt{3}-x})$$ The code is Integrate[a/x*E^(b/(3^0.5 - x)), {x, 1, 3^0.5}] But it can't work ...
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1answer
54 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 = ...
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1answer
55 views

Integrand evaluating to non-numerical values

I have solved a system of equations using NDSolve just fine. From there, I can plot the solutions $u(x)$ and $v(x)$, as well as its derivatives, just fine. But, when I want to evaluate the energy ...
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1answer
48 views

How can I fix my code so NIntegrate doesn't produce error message?

I get this error when trying to integrate a seemingly simple expression: ...
0
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1answer
54 views

NDSolve with arrays and Tables of Equations and WhenEvent

I've been toying around with NDSolve for a while, and read through the website. By doing so I discovered that I could use it for vectors and arrays with much pleasure. So I wanted to write a simple ...
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1answer
92 views

Multiple NIntegral with singularity

I need to compute the following integral FF[0]. When evaluating FF[0] Mathematica simply takes too much time. The problem may ...
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1answer
114 views

Initial and boundary value errors

NDSolve::ivone: Boundary values may only be specified for one independent variable. Initial values may only be specified at one value of the other independent variable. >> I keep getting this, ...
0
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1answer
152 views

Using NDSolve for three variables as function of time

I want to be able to plot z, and r. Should I be using DSolve, NDSolve or something else? I've tried to clear it up a bit Thanks, Will ...
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1answer
141 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: ...
0
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1answer
177 views

How to improve the performance of this code

I have implemented a code in Mathematica 9 to simulate a scattering problem, and I got really disappointed about its performance when compared to Matlab. Since I am a newbie in Mathematica, would ...
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1answer
99 views

Transformation of the NDSolve result into new dependent variables

I have solved a set of coupled differential equations and now I need to convert them into different dependent variables and sketch their trajectories. Here is the code I have written so far: ...
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1answer
181 views

Fitting a Function With a Numerical Integral [duplicate]

I am having trouble using FindFit with the following function. ...
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1answer
90 views

PDE plotting assistance needed

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1answer
138 views

PDE Solving in mathematica

I'd like to ask how I might go about solving this equation: $\frac{\partial Ci}{\partial t} + \frac{1}{r^2}\frac{\partial (r^2 Ci)}{\partial r} = D\frac{1}{r^2}\frac{\partial}{\partial ...
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1answer
334 views

Syntax question regarding Triple Integrals in Mathematica

Integrate[1, {z, 0, 5}, {x, -Sqrt[ 9 - y^2], Sqrt[ 9 - y^2]} , {y, -3, 3}] 60 Sqrt[9 - y^2] How comes I am not getting a number for my final answer? This ...
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1answer
95 views

Order of evaluation in nested expression

I am trying to make a function that works as follows: Integrate 1 for all t in the interval $ [0,1] $ such that the first element of function vstar is positive. ...
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1answer
163 views

find derivative with defined function

s[a_, b_] := NDSolve[{y''[x] == y[x] Cos[x + y[x]], y[0] == a, y'[0] == 1}, y, {x,0, b}] I need to find the minimal of $\int _1^by[x]^2$ in the region ...
0
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1answer
170 views

Fast integration of 2D distribution across lines parallel to y-axis

I'm struggling with a small data set and a slow calculation. I have hundreds of small 2D data arrays and need to integrate across several lines parallel to the y-axis. Let me start with the data ...
0
votes
1answer
211 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
143 views

Error messages when using NInverseFourierTransform

I have two functions that I need to inverse Fourier transform and I was trying to get Mathematica to help me. I tried simply using theInverseFourierTransform ...
0
votes
2answers
257 views

Problems with NDSolve and stiffness

I am trying to solve an ODE in chemical kinetics: $$\begin{align*} \frac{\mathrm d[x]}{\mathrm dt} &= -k_1 [x][y]\\ \frac{\mathrm d[y]}{\mathrm dt} &= k_1 [x][y] - k_3[y] \end{align*}$$ My ...
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votes
1answer
219 views

double integration

I want to evaluate a double integral, but the limits of one integral is a function of the second. Like this ...
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1answer
311 views

Integrate on a logarithmic grid

I am trying to solve numerically an integral equation, and from a couple of tests I can see that the result has a strong logarithmic divergence. For my specific problem it is very important to have ...
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1answer
305 views

Applying l'Hôpital's Rule to NDSolve with Piecewise Function

OK, so I've been working on this problem for over a week and it's driving me crazy. I'm trying to solve a system of two differential equations in $x(t)$ and $y(t)$ using a "time-elimination method," ...
0
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1answer
76 views

Error with minimization of NProbability

I'm trying to solve the following problem: ...
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1answer
600 views

Nested NIntegrate - NIntegrate::inum: - error

I have the problem quite similar as in: Nested NIntegrate I define two functions: ...
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1answer
118 views

How to change variable that has been defined in PDE?

I have a PDE function that contains a variable (named ka). I want to plot the result of my PDE in 1 plot using several different ka values. However, I'm not sure about how to write down this equation. ...
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2answers
210 views

System of ODEs specified by large coefficient matrices

What is the best way to call NDSolve for solving a system of differential equations of the form ...
0
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1answer
288 views

NDSolve event handler Question [closed]

I'm trying to plot a ball falling, hitting the ground and coming back up. without air friction, the equations for the system would be ...
0
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1answer
332 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
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1answer
236 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 ...
0
votes
2answers
290 views

NDSolve and results of the previous computations

I want to solve following system of ODEs: $ \Bigg\{ \begin{array}{} \frac{\partial C}{\partial t}=\frac{2W_b}{Rsin(\theta)}(1-\frac{C}{\gamma})+\frac{\nu}{\pi R^2}\frac{\partial C}{\partial Z} ...
0
votes
0answers
30 views

Plotting and NIntegrate [on hold]

I have a problem. I try to make such a plot: function = y^(3/2)*Exp[I t y - y^2]; Plot[NIntegrate[function, {y, -∞, ∞}], {t, -20, 20}] But I have no plot - I ...
0
votes
0answers
38 views

How to calculate the analytical result of this double integral?

I'm trying to solve this double integral: $I(a,b)=\displaystyle{\int_{-1}^{1}dy\int_1^{\infty } \dfrac{y\left(x^2-1\right) e^{-ax} }{b-\frac{\sqrt{x^2-1}}{x}y} \, dx} \,\, ...
0
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0answers
25 views

Calculating Muliti-integral Time-Ordering operator [migrated]

I am trying to solve the time-ordering operator Like this: $S(t)=\mathcal{T}e^{\int_0^tduA(u)\int_0^udvB(v)}S(0)$. How can I calculate S(t) with minimum error?