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# Ivan van der Kroon

### Twente University

Active since 2011

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How to avoid Excel using Matlab
Hey, I am about to finish my studies and with it, probably, my Matlab usage, as most employers favor Excel. I was looking for me...

11 years ago | 1 answer | 0

### 1

programming a PDE in Matlab
You already have written it in a ode-form, i.e. first temporal derivative on LHS. The RHS only needs the correct implementation ...

11 years ago | 0

Problem with matlab
Your function should assign values to m and X depending on the value of t. Note that t in the solver can take any value in your ...

12 years ago | 1

Using an iterative method with scalar functions/function handles (help me fix this code)
In the doc of fzero 'Find root of continuous function of one variable', which you clearly need here. Doc of minres 'find a mi...

12 years ago | 0

How can I select between two solutions?
This is a standard quadratic formula, put it in the form a*y^2+b*y+c=0 and the solutions are y1=(-b+sqrt(b^2-4*a*c)...

12 years ago | 0

How to obtain accurate fast fourier transformation
For your frequencies, you make a mistake in your frequency array fs=Datapoints/Length; f = fs/2*linspace(0,1,NFFT/2+1); ...

12 years ago | 1

| accepted

This is not a very nice solution, but it worked for me fid=fopen('test.txt'); C = textscan(fid, '%s'); C=C{1}; a=[]; fo...

12 years ago | 1

Simulation of charged particle in matlab
You probably want to have something like fun=@(t,x) [x(4:6);cross(x(4:6),q/m*B)]; t=linspace(0,tend,1e3); [t,x]=ode45(fun...

12 years ago | 1

How can I convert a system with delay from continuous to discrete and from discrete to continuous and the result be the same?
In that case the sample time in tf should be an integer times the sample time in c2d. You can try it for arbitrary a and integer...

12 years ago | 1

nonlinear least squares fit
t is a row-vector while data is a column-vector. Change it to t=(1:n)'; Btw, I got x= 0.0012 0.1046 -7...

12 years ago | 0

Double Prime
xlabel('test''''') gives you an xlabel as test'' You need double primes in strings for a single prime.

12 years ago | 0

mldivide error
./ for right and .\ for left division

12 years ago | 0

Replace zeros with NaN's - when there are already NaN's in the matrix?
Change to double first: F=double(F); F(find(~F))=NaN; Just curious; why would you need this?

12 years ago | 0

how can I convert a string to an expression which "symvar" can search for identifiers?
insertfunction='cos(pi*x - beta1)' >> symvar(insertfunction) ans = 'beta1' 'x'

12 years ago | 1

Out of memory using mrdivide
Short about inv(B); it has 191*2+1 diagonals (36288/189=192, but this is for one of the triangles and includes the main diagonal...

12 years ago | 0

How to replace the elements of a matrix using the conditions if,else?
Just implement it for multiple matrices using element multplication: Logical=(L>0.5).*(M==0).*(N<0.5); T=-Logical+(M+1)....

12 years ago | 0

How to replace the elements of a matrix using the conditions if,else?
You don;t need the if-statment here but only the logicals. This gives you a matrix with ones where X is larger than 0.5 and zero...

12 years ago | 1

Optimal arrangement of a small vector within a lager vector
Allow me to define: N=length(b); M=length(a); Q=3;%number if placements p0=ones(Q,1);%starting vector for placements w0...

12 years ago | 1

Out of memory using mrdivide
Some follow-ups: a) Where do you need this for? Your result will lose much of its sparcity. Maybe if you post your entire pro...

12 years ago | 1

How to create sounds with specific characteristics?
A window can be anything going from zero to unity. In this case it should reach unity after 5ms from the start. You should know ...

12 years ago | 0

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Discrete Fourier Transform of large data sets
Is the size of the result a problem too? Otherwise you can add zeros to a segment perform the transform and in the end take the ...

12 years ago | 0

| accepted

Out of memory using mrdivide
I agree with Jan; if you have the same number of non-zero elements you probably filled the main diagonal. In that case spdiags w...

12 years ago | 0

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Why do i have to take the abs when using fft and ifft?
Walter means that discrete Fourier transforms are not exactly as what one would expect from their continuous counterparts. You c...

12 years ago | 0

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How do I reset axis ticks to normal after I modify them?
You can use set(gca,'XTickLabel',xdate) where xdate is your x-axis data. With datetick you're just changing the labels,...

12 years ago | 0

row-echelon matrix form (not reduced)
With rref you will produce the reduced row echelon form, see doc rref But a non-reduced form is not unique. See for ins...

12 years ago | 1

How do I find the boundaries of a value in a matrix?
[rows,cols]=find(I==8) rows = 3 2 3 4 2 1 2 cols = 2 3 ...

12 years ago | 2

How to plot frequency response in matlab
you could get familiar with the wintool and wvtool gui's. I think these tools are really straight forward. Good luck!

12 years ago | 0

How to make a 0.001 difference ?
a=1:100; b=sort([a a+0.001]);

12 years ago | 0

| accepted