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Michael Völker


32 total contributions since 2011

Professional Interests: signal processing in MRI

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Submitted


A safety net for MATLAB's clear command
intercept amok calls to clear() in interactive mode

1 year ago | 1 downloads |

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Responded


Re: How Comparing a BIG matrix with itself after execution "while loops"? (no loss of memory)
For me (R2014a, Linux), calling isequal(O,Onew) does not require more memory than idling around with those arrays in the workspa...

2 years ago | 1193 views

Responded


Re: speed of matrix multiplication
My tests were in 2014a on a 8-core Xeon server (2 quadcore CPUs). With 2012a, the direct multiplication is stil slower (but 1s f...

2 years ago | 2230 views

Responded


Re: speed of matrix multiplication
Bruno, thanks for your reply. I attempted to think about the implementation, too; but since mtimes() uses optimized LAPACK lib...

2 years ago | 2230 views

Posted


speed of matrix multiplication
Hi, I found a really weird performance issue with mtimes for pretty large matrices. Look at my test function. A better formatt...

2 years ago | 2230 views

Answered
how do I plot one channel of data when I have 100 channels?
data = randn(100,300); % bad example for actual data channel = 76; % select channel to plot figure, plot(...

3 years ago | 0

| accepted

Submitted


simulate motion in Cartesian MRI
Simulates Point Spread Function (PSF) and k-space data for motion in Cartesian sequences.

3 years ago | 7 downloads |

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MRI Partial Fourier reconstruction with POCS
Fast and robust reconstruction of Cartesian partial Fourier MRI data with POCS

4 years ago | 23 downloads |

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Submitted


hypersphere / n-sphere
Generate n-dimensional Ellipsoid or Sphere

4 years ago | 9 downloads |

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Submitted


Execute default function of a MATLAB installation
Execute the default function available as an m-file in MATLAB's installation directory.

4 years ago | 0 downloads |

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Answered
To find the maximum value in a matrix?
more general: |max(A(:))|

4 years ago | 6

| accepted

Responded


Re: contourf() strange with only few levels
Armin, I created a wrapper for the colormap function, intended to use more shadings: http://www.mathworks.com/matlabcentral/fil...

4 years ago | 2703 views

Submitted


sub2allind
convert subscripts to ALL corresponding indices

5 years ago | 1 downloads |

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Solved


Finding Perfect Squares
Given a vector of numbers, return true if one of the numbers is a square of one of the other numbers. Otherwise return false. E...

5 years ago

Solved


Triangle Numbers
Triangle numbers are the sums of successive integers. So 6 is a triangle number because 6 = 1 + 2 + 3 which can be displa...

5 years ago

Solved


Summing digits
Given n, find the sum of the digits that make up 2^n. Example: Input n = 7 Output b = 11 since 2^7 = 128, and 1 + ...

5 years ago

Solved


Remove the vowels
Remove all the vowels in the given phrase. Example: Input s1 = 'Jack and Jill went up the hill' Output s2 is 'Jck nd Jll wn...

5 years ago

Solved


Select every other element of a vector
Write a function which returns every other element of the vector passed in. That is, it returns the all odd-numbered elements, s...

5 years ago

Solved


Swap the first and last columns
Flip the outermost columns of matrix A, so that the first column becomes the last and the last column becomes the first. All oth...

5 years ago

Solved


Column Removal
Remove the nth column from input matrix A and return the resulting matrix in output B. So if A = [1 2 3; 4 5 6]; and ...

5 years ago

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...

5 years ago

Solved


Who Has the Most Change?
You have a matrix for which each row is a person and the columns represent the number of quarters, nickels, dimes, and pennies t...

5 years ago

Solved


Find all elements less than 0 or greater than 10 and replace them with NaN
Given an input vector x, find all elements of x less than 0 or greater than 10 and replace them with NaN. Example: Input ...

5 years ago

Solved


Make a checkerboard matrix
Given an integer n, make an n-by-n matrix made up of alternating ones and zeros as shown below. The a(1,1) should be 1. Example...

5 years ago

Solved


Determine if input is odd
Given the input n, return true if n is odd or false if n is even.

5 years ago

Solved


Find the sum of all the numbers of the input vector
Find the sum of all the numbers of the input vector x. Examples: Input x = [1 2 3 5] Output y is 11 Input x ...

5 years ago

Responded


Re: Info about omitted 1st output from within function
It seems that you are right from a practical point of view. My problem is rather large and computationally demanding, with typic...

5 years ago | 2367 views

Responded


Re: Info about omitted 1st output from within function
You are totally right, a&b together is much faster than one after another. But as I wrote earlier, 'a' and 'b' are the outputs o...

5 years ago | 2367 views

Responded


Re: Info about omitted 1st output from within function
Right, that's what I'm doing now, instead. This is just starting to get quite messy, because myfun() is a cost function of the f...

5 years ago | 2367 views

Responded


Thanks (Re: Info about omitted 1st output from within function)
Okay, that is at least a plain and useful answer. Thanks.

5 years ago | 2367 views

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