# Matz Johansson Bergström

### Chalmers University of Technology

Check out my website: www.matzjb.se for tips on various coding-related problems.

Professional Interests: image processing, algorithms, computer graphics, high performance computing.

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**Content Feed**

reason for converting image into double

The reason is precision. Say you read an image using (write this in the Matlab prompt) >>Im = imread('filename'); >>clas...

7 years ago | 1

why slow 5 times when tic or toc and expression in one line?

Funny enough I also get horrible timings. I am using Matlab 2014a and I get: Elapsed time is 1.053381 seconds. Elapsed t...

7 years ago | 0

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How can I fill a matrix column with dta coming from another matrix according to index

Without knowing the size of the matrix, it might be a good idea to use a sparse matrix, instead of filling the non existant elem...

7 years ago | 1

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Permutation of array elements

This seems to work A = {'test a 1', 'test a 2'}; B = {'test b 1', 'test b 2'}; WAKE = [A',B'] %see below for explanat...

7 years ago | 0

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How to perform skull stripping using matlab?

I found something that might be of help: <http://se.mathworks.com/help/matlab/visualize/exploring-volumes-with-slice-planes.htm...

7 years ago | 1

using mex -setup error

As the error message says you are missing a suitable compiler to create mex files. See <http://se.mathworks.com/help/matlab/matl...

7 years ago | 0

How can I insert row into matrix without deleting its values?

The only way I know of is to create a new matrix consisting of A and the row and then append the three matrices together, for in...

7 years ago | 15

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How to solve the problem Ax=b, when A is (14400,14400) and b (14400,1)?

If A is full \ has to perform a Gaussian elimination. A is ~1.5GB in double precision and it seems that \ requires at least that...

7 years ago | 0

I was record on my phone a sound. how to hear that sound in matlab.

I found a matlab script (with exe and library) that can import m4a files. I tried it and it seems to work. See <http://www.ee.co...

7 years ago | 0

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how can obtain min of matrix

This solution is maybe a little ugly, but it works Say that A is the matrix. tmp = A; %we will destroy elements, ...

7 years ago | 0

How to solve this equation?

This is actually very simple using the *\* operator, see <http://se.mathworks.com/help/matlab/ref/mldivide.html mldivide,\ docum...

7 years ago | 0

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Multi-Line Colors in 2014

That's odd. I'm using Matlab R2014a and it seems to be working fine. Are you using Matlab R2014b?

7 years ago | 1

what is the difference between a vector and a matrix?

A matrix is simply a rectangular array of numbers and a vector is a row (or column) of a matrix. Read more about the practica...

7 years ago | 3

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How can I get different 2D Matrices from a 3D matrix?

The size of the A(1,:,:) will be a 1-by-n-by-z matrix, so you have to temporarily store it in a 2d matrix tmp(:,:) = A(1,:,...

7 years ago | 0

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how to crop an image

In my answer I throw away the green and blue channels of the PNG, because it is black/white. If you want to use a color image, t...

7 years ago | 2

How to read data one by one

It should be sufficient to write filename='coordinates.txt'; [x,y,z] = dataread('file', filename, '%f%f%f', 'del...

7 years ago | 0

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FFT manual help formulation

The range 1:50 is only used in the plot, not in the rest of the example. See <http://se.mathworks.com/help/matlab/ref/fft.html ...

7 years ago | 0

Replacing non-alphabetic characters with numbers?

Yet another answer, just for the "cellfun" of it ;-) tmp = cellfun(@(x) isstrprop(x, 'alpha'), {TS1}, 'UniformOutput', fals...

7 years ago | 0

how can i read hdr file?

Have you tried http://www.mathworks.se/help/images/ref/hdrread.html?

8 years ago | 0

Assigning colors on a cylinder

Simplest way [x,y,z] = cylinder; surface(x,y,z, 'FaceColor','texturemap',... 'EdgeColor','none','Cdata', rand(10)...

8 years ago | 1

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How to find first ten prime numbers that are greater than 4?

You could do it like this x = primes(100); %pick primes smaller than, say 100 x = x(x>4); %pick the ones larger than 4 ...

8 years ago | 0

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Why aren't my cases working correctly

I would put period and t calculation outside of the switch and I think you want t = linspace(0,period*cycles,100);

8 years ago | 0

Index through datestring, selecting whole hours

Another alternative where I just pick the last two characters from the first column of the cell: %mock data: cel{1,1...

8 years ago | 0

How can I improve Matlab perfomance for this code?

It seems to me that combntns (which is the same as nchoosek) is taking a long time to finish. So, the appending of the combinati...

8 years ago | 0

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how to integrate inside 'for' loop

To solve this problem you can use a anonymous function handle to a function with x and n as arguments. f = @(x) myfun(x, ...

8 years ago | 0

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Plotting a 3D matrix graph

First, I assume that the graph is undirected, edges are going both ways, but you might want to change that maybe. A =...

8 years ago | 0

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access values in dataset

LinearModel is using tables, so you can write tmp = table2array(Im.Coefficients) and access tmp.

8 years ago | 0

Color code with dash line

x=1:10; plot(x, cos(x), ':','color',[0,0.5,0],'linewidth',3)

8 years ago | 2

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what does c(:).' mean? c should be a vector

By writing c(:)' you are making sure that the vector has the dimension 1xn, where n is the length of the vector, a row vector. H...

8 years ago | 1

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how to create 200 random matrices using loop..

I have not tried it but something like this: n=200; tmp = rand(32,32,n); and then to multiply each matrix for i...

8 years ago | 0