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# Niles Martinsen

Active since 2012

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Speeding up nested for-loop
Hi I have the following nested for-loop, containing some if-statements. It is running horribly slow, so I would be very happy...

6 years ago | 0 answers | 0

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Precision issues when going from Fortran to Matlab
Hi I have a piece of code written in Fortran that I have now finished writing in Matlab. They do exactly the same calculation...

7 years ago | 1 answer | 0

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Declaring variables with high precision
Hi I have the following piece of code that I have also implemented in Fortran. According to Fortran the variable *Ax(3,6,4)* ...

7 years ago | 1 answer | 0

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Question

discrete deriviative has wrong sign
I have the following MWE that calculates the derivative of a function along the y-direction: x=1:50; y=x; phi = s...

7 years ago | 1 answer | 0

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Question

Solve equation with 1 unknown numerically
I have the following script that defines a function and sets up and equation: H = @(f) sum(log(f)); f = rand(1, 1...

8 years ago | 1 answer | 0

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Question

Generating numbers according to a modified Gaussian
Hi I am trying to generate numbers following a probability-distribution given by the 1D Maxwell velocity distribution, which ...

9 years ago | 0 answers | 0

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Nonlinear fit with constraints in R2012b
Hi I am running R2012b and doing nonlinear weighted regression as explained here: http://www.mathworks.se/help/stats/examples...

9 years ago | 3 answers | 0

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Nonlinear fit to data with errors in both coordinates
Hi I have a set of data (x, y), where there are measurement errors on both coordinates. These errors are non-constant, and I ...

9 years ago | 0 answers | 0

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Question

Solving very stiff system of ODE's
Hi I have the following system of ODEs (a very stiff system!): eoms = @(t,x) [ 3.9e3 + 4.8e4*x(3) - 3.9e3*0.02*...

9 years ago | 1 answer | 0

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Question

Solving coupled ODE's by ode45
Hi I have a relatively simple set of coupled ODE's that I am trying to solve by ODE45. The following is the content of the .m...

9 years ago | 3 answers | 1

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Question

Remove every second tick on y-axis
Hi I have the following code x=-6:0.1:6; figure(1) plot(x, (1)./(1+4*x.^2), 'b') grid on When I plot this, t...

9 years ago | 1 answer | 0

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Question

Hi I am trying to evaluate the following integral numerically in MatLAB: http://www.scribd.com/doc/100400549/mwe However, ...

10 years ago | 1 answer | 0

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Solved

Make the vector [1 2 3 4 5 6 7 8 9 10]
In MATLAB, you create a vector by enclosing the elements in square brackets like so: x = [1 2 3 4] Commas are optional, s...

10 years ago

Question

Evaluate advanced integral numerically in Cartesian coordinates
Hi I have previously asked a question regarding how to evaluate a specific integral in MatLAB, see this thread: http://mathwo...

10 years ago | 0 answers | 0

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Question

Plotting multi valued data properly
Hi Please take a look at my dataset here: <http://peecee.dk/upload/view/377379> It can be plotted using the following ...

10 years ago | 1 answer | 0

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Question

Fit parameter not changed
Hi I am trying to fit a function to some data points. My code is the following: clc clear all close all for...

10 years ago | 1 answer | 0

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Thanks for taking the time to write all that. That is very kind of you, and it gave me a big push in the right direction. Thanks...

10 years ago | 0

Question

Hi I am trying to evaluate the following integral in MATLAB: http://www.scribd.com/doc/100400549/mwe However I haven't had...

10 years ago | 3 answers | 0

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Question

Nonlinear Fitting: Extreme uncertainties on a very good fit
Hi I have some data (x, y) (no uncertainties on either x or y), which very nicely follows an exponentially decaying function....

10 years ago | 1 answer | 0

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Question

Break in the axis
Hi I have a plot of data points (x, y). The issue is that one of the first data points has a very large amplitude, whereas th...

10 years ago | 4 answers | 1

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Question

Changing the vertical errorbar tee
Hi I have the following example x=1:1e1; y=x; e=sqrt(y); figure(1) errorbar(x, y, e, e) What I want is to...

10 years ago | 1 answer | 0

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Question

Linear fit with data uncertainty
Hi Fitting a polynomial in Matlab to some data (x, y) is easy using polyfit as e.g. p_RvsT = polyfit(r_vs_t(:, 1), r_vs_...

10 years ago | 1 answer | 0

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Question

Polyfit and parameter uncertainty
Hi I have some data (x, y), where y is proportional to x. I want to find the relationship, so I fit a function of the form f(...

10 years ago | 1 answer | 0

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Question

Fitting with nlinfit
Hi I am fitting a function to some data using nlinfit in the following way [b, r, J, COVB, mse] = nlinfit(v(:, 1), v(:, ...

10 years ago | 1 answer | 2

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Fitting a convolution
Andrei's suggestion works, but when I increase the resolution of x, then the convolution changes as well. Is this just a propert...

10 years ago | 0

Question

Fitting a convolution
Hi I have the following piece of code: ---------------------------------------------------------------------------------...

10 years ago | 2 answers | 0

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Fitting data with two peaks
If I use this approach http://www.mathworks.se/support/solutions/en/data/1-GNRWCU/index.html, is there a way to obtain the error...

10 years ago | 0

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Fitting data with two peaks
Hi I have some data, which is not too different from the top graph in this picture: http://www.aanda.org/index.php?option=com...

10 years ago | 5 answers | 0

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Question

Normalize data set
Hi I have a data set giving me (time, voltage), and I wish to normalize the data set. Is there a smart way to do this in MatL...

10 years ago | 2 answers | 0

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Question

Fitting in MatLAB
Hi I have a dataset, which I am trying to fit to a function having the form A*cos(a*x) + B*sin(b*x) + C/x + exp(-D*x). ...

10 years ago | 1 answer | 0