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# Bruno Luong

##### Last seen: Today
1,101 total contributions since 2009

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Conditional Random number generation
m = 5; n = 3; s = 10; This will generate uniform distribution with sum criteria % generate non-negative integer random (m x ...

2 hours ago | 0

Rounded random numbers with fixed sum
k = 3; r = (diff([0 sort(randperm(100+k-1,k-1)) 100+k])-1)/100

3 hours ago | 0

mex-file crashes MATLAB in for loop
Those are wrong, you should not Free the pointers that you are not Malloc. mxFree(a_double); mxFree(b_double); mxFree(z_do...

11 hours ago | 1

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C = union( A,B ) is too slow. Is there any faster way given that A and B are ordered.
If you have a decend C-compiler you might use my MEX MERGE SORTED ARRAY c = mergesa(a,b); % or mergemex(a,b); c = c([true; dif...

12 hours ago | 1

Recover matrix Z from XZX', Z es symmetric and n-by-n, while X is k-by-n where n>>k
You can't getback to 27x27 covariance matrix Z after reducing it it on 5 dimensional space (by X). The information lost forevver...

1 day ago | 0

solve A*X=B containing very large or small elements
Work with unitless system, scale your matrix, or use automatic scaling if you don't want to bother.

1 day ago | 0

How do I shift columns (left or right) in a matrix
k > 0 shift right k < 0 shift left A*diag(ones(1,size(A,2)-abs(k)),k)

1 day ago | 0

How to solve the equation of binary logic operation, where all unknowns are 0 or 1
[x1,x2,x3,x4,x5,x6]=ndgrid(0:1); x1 = x1(:); x2 = x2(:); x3 = x3(:); x4 = x4(:); x5 = x5(:); x6 = x6(:); b = [x1+x2+x3+...

2 days ago | 0

Finding the most orthogonal set of n vectors from dataset of unit vectors
I propose this % random test A, which represents 100 normalized vector in R^5 n = 5; m = 100; A = randn(n,m); A = A ./ sqrt...

2 days ago | 0

EVALIN cannot execute a return?
Yes it is written in the doc. From EVALIN/EVAL document page "evalin(workspace,expression) ... expression — Expression to ev...

3 days ago | 1

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Matrix compare and unkonw relationships to find
Use regression methods. If you have a linear/affine model, then use linear algebra. If you have "kind" non-linear, use polynomia...

3 days ago | 0

Why is memory reduced for an identical copy of a sparse array?
Nah nothing to do with name length, it's the number of internal non zeros of ('Ir" and "Pr" old notation) array reserved by MATL...

3 days ago | 1

(Block-) Matrix multiplication inaccuracy
Same problem, don't count on exact associativity when working with floating point arithmetics. I can quote word-to-word from wha...

3 days ago | 0

Reshape n-th dimension of an array
You operation makes the array changing its size, you can't use for-loop to store the rotated page in the SAME arrray. And btw f...

3 days ago | 1

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Curl, Divergence calculation from velocity data
Your data is already gridded, no need to gridded on top of it load('matlab.mat') UU=reshape(data(:,3),[75 62]); VV=reshape(...

3 days ago | 0

Checking a matrix for duplicates in specific row, removing the respective columns
d= [1 2 2 3 4 5 6 6 7; 1 2 3 4 5 6 7 7 8] dd = diff([nan,d(1,:),nan])==0; remove = dd(1:end-1) | dd(2:end) x_cut = uni...

4 days ago | 0

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Interpolating at vertices of a mesh
In theory you cannot. A function that is piecewise constant on elements is discontinuos at the vertices and you cannot speak ab...

4 days ago | 0

Obtain the mean angle (circle mean of a file)

5 days ago | 0

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How parentheses effects multiplication with pi ?
From wikipedia "While floating-point addition and multiplication are both commutative (a + b = b + a and a × b = b × a), they a...

5 days ago | 0

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% Replace this with your image Image100 = peaks(100)+10; %Centering padding in 4 sides PadImage300 = zeros(300,300,size(Ima...

5 days ago | 0

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How to create a surface with random spheres protruding?
Is this you want? x = linspace(0,1); y = linspace(0,1); [X,Y] = meshgrid(x,y); Z = zeros(size(X)); N = 30; for k=1:N ...

5 days ago | 0

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Integral calculation using matlab
Feel free to change these hyper-parameters n = 3 k = 2*pi*rand() integral(@(phi) arrayfun(@(phi) abs(integral(@(theta) exp(...

6 days ago | 0

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Combining function handles into one function handle
a = @(x) x(1)^2+x(2)^2; b = @(x) x(3)^2-x(4)^2; c = @(x) x(1)*x(4); % suppose your for-loop puts each function handle in a ...

6 days ago | 0

I cannot find the distance between two matrices with respect to the Frobenius inner product.
Distance in frobenius scalar product: dist_AB = norm(A - B, 'fro') which is the same as this norm(A(:)-B(:),2)

6 days ago | 0

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Indexing problem with matrices
A = [3 5 9 6 ; 2 1 13 6 ; 6 8 52 4 ; 13 6 8 22 ]; GRID = [linspace(1,100,100); rand(1,100); rand(1,100)]' Code [tf,loc]=ismem...

6 days ago | 0

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Convolution of to matrices
Example t1 = 0:2; A1 = [0.25 0.5 0.25]; t2 = [0 3 6]; A2 = [0.25 0.5 0.25]; Code for convolution vector Y (t,A) (I don't kn...

6 days ago | 0

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How do I turn of thr grid of a surface but keep the edge line on?
Just serve yourself with plot3 commands [X,Y,Z] = peaks; surf(X,Y,Z,'edgecolor','none'); hold on plot3(X(1,:),Y(1,:),Z(1,:),...

6 days ago | 1

Select points inside a polygon

6 days ago | 1

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Select points inside a polygon
But you already have the index in your code. here ... inon = in | on; % Combine .i...

6 days ago | 1