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Christopher


Macquarie University

Active since 2014

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Performance of cell arrays, multi-dimensional arrays, structure arrays, and multiple variables
I've found that the performance of cell Arrays, multi-dimensional arrays, and structure arrays are all far slower than the use o...

4 years ago | 1 answer | 1

1

answer

Question


MEX file maker not working when using < thread > header
I've made a fast version of accumarray in C++ and am trying to make a MEX file for it, but it is not working. I can compile m...

4 years ago | 0 answers | 0

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answers

Question


Is it possible to avoid copy-on-write behavior in functions yet?
As I understand, MATLAB has used a system called 'copy-on-write' for function calls. So if you have a function of the form f...

4 years ago | 3 answers | 3

3

answers

Question


Performance of MATLAB instances over time
I've noticed for a long time that the performance of a matlab instance seems to decrease with use. I presently am seeing this ef...

4 years ago | 2 answers | 0

2

answers

Question


Sharing Large Memory Variable in a parfor
I have a code which uses a very large variable of size [3 10 61 50 50 50 60], which is about 55 Gb. The form of the code is roug...

6 years ago | 0 answers | 0

0

answers

Question


Fastest method of modifying elements of a matrix based on multiple indexes
I am trying to arrive at the fastest method of modifying the elements of a matrix based on more than 1 index for the elements in...

6 years ago | 0 answers | 0

0

answers

Question


How does Matlab use less memory after exceeding physical limit?
I have a code which normally requires about 17 GB of memory, since there is a matrix which is about 12+ GB which is continually ...

6 years ago | 0 answers | 0

0

answers

Question


Reduce memory requirement of some vectorized operations
In the following code, i perform some vectorized operations which happen to be highly memory intensive because my actual value o...

6 years ago | 0 answers | 0

0

answers

Question


gather data from different sections of each column
Consider the code: totmods = 10000; numselect = 1000; A = rand(100,totmods); % numbers B = randi(90,10,1000)...

6 years ago | 3 answers | 0

3

answers

Question


parfor works on local computer but not on a cluster
My code has the following form: clear all rng('shuffle') runtables = importdata('runtable.mat'); % a 40000x22 table of...

6 years ago | 0 answers | 0

0

answers

Question


Does matlab become slow and unusable when working in a folder with many files?
Matlab has recently become incredibly slow and virtually unusable recently. Particulary, functions such as importdata(sprin...

6 years ago | 2 answers | 0

2

answers

Question


logical operations on particular matrix elements
I have the following code: numels = 7; numpts = 3; C = sparse(numpts,numels) A = randi(numels,[numpts,1]); B = r...

6 years ago | 1 answer | 0

1

answer

Question


Optimising code to get matrix indices based on point coordinates
I have the code xnum = 600; xstp = 1/(xnum-1); xgrid = 0:xstp:1; ynum = 600; ystp = 1/(ynum-1); ygrid = 0:xstp...

6 years ago | 2 answers | 0

2

answers

Question


How to implement a parfor in place of a for loop?
I understand the idea behind what is and isn't allowed in a parfor loop, but I do not understand the practical application. I ha...

6 years ago | 0 answers | 0

0

answers

Question


Colormap not working: is it too long?
When I use the following colormap, cmap1, I only get two colors displayed in my figure. Why does Matlab hate my colormap? c...

6 years ago | 1 answer | 0

1

answer

Question


Need to get rid of an eval and loop
I have the code Fe = zeros(maxthick,numfiles); for i=1:numfiles eval(sprintf('tnum = numel(data%d.results(:,13));',i)...

7 years ago | 1 answer | 0

1

answer

Question


creating strings with variables
I have to access many different files with slightly different names and instead of manually writing them in matlab I want to dyn...

7 years ago | 2 answers | 0

2

answers

Question


Can I speed up an ismember operation?
I have a list of 100 random numbers 1-10: numpoints = 100; gridnum = 10; grid_ind = randi(gridnum,[numpoints 1]); % 100 ...

7 years ago | 1 answer | 0

1

answer

Question


Using Matlab in 4K resolution
I am using windows 8.1 and Matlab r2014a on a new 4K screen. One of the reasons for this is because I want to be able to view mo...

7 years ago | 2 answers | 1

2

answers

Question


Data lost in saved file
I have a code which periodically saves many .mat files. e.g.: save( filename, 'P_hist', 'O_hist', 'Osums_hist' ... ...

7 years ago | 0 answers | 0

0

answers

Question


Can't append variables to large .mat files?
I am using R2013b. I have the code: save(savefilename, 'newP_hist', 'newO_hist', 'newE_hist', 'newt_hist'); save(savefilen...

7 years ago | 1 answer | 0

1

answer

Question


collect rows of a matrix having a desired number in the first row
If I have a matrix, what is the fastest way to collect the columns which satisfy a logical operation in the first row? So if ...

7 years ago | 1 answer | 0

1

answer

Question


How can I quickly create movies?
I have a large code which generates several 120x120 matrices which I want to systematically record and make a movie out of. Bec...

7 years ago | 0 answers | 0

0

answers

Question


Optomize a vectorized code
I have a vectorized code. It runs fast (I think), but I would benefit enormously from reducing its computational cost. I have a...

7 years ago | 0 answers | 0

0

answers

Question


How to close executable called with dos()
I am using dos('thermo.exe') to run the executable. This exe does something and then spits out a text file of results. ...

7 years ago | 0 answers | 0

0

answers

Question


number of elements of each unique values in a matrix
I can use unique(A) to get an array of each unique value in the matrix A. However, how can I also get an array of the number of...

7 years ago | 1 answer | 0

1

answer

Question


Create matrix with randomly distributed integers, with exact relative abundances
I want to create a matrix of randomly distributed integers between 0 and 4 (0, 1, 2, 3, or 4). However, I want the abundance of...

7 years ago | 1 answer | 0

1

answer

Question


problem getting correct indices of a matrix
I have the code: odif = find(o~=on); % element index: combos with O==O pdif = find(p(odif)~=pn...

7 years ago | 1 answer | 0

1

answer

Question


Sum elements in matrix if equal to value in another element
I have the matrix OVEC, which consists of a number of column vectors with numbers How do I sum all the elements in each colum...

7 years ago | 2 answers | 0

2

answers

Question


Fast sampling every other element in a matrix
I have a matrix M. I want to delete every other column and every other row. However, I already know how to do this as: M ...

7 years ago | 1 answer | 0

1

answer

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