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Equivalent of c++'s NULL or python' s None in MATLAB
If you use recent MATLAB you can use also missing and ismissing

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How to change number precision with writestruct
The number of significant digits of writestruct is quite limited, as showed by this example s=struct('pi',pi); writestruct(s,...

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Replace nested loops with a matrix
i=2:nhx-1; j=2:nhy-1; U(i,j)= U(i,j)-dt*(Pc(i+1,j)-Pc(i-1,j))/(2*hx);

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Get indices of all rows containing a value - repeated or not
[c,~,J] = unique(sort(connections,2),'rows'); [i,~,I] = unique(c); [~,j] = ismember(i, id); xy = [x(j) y(j)]; I = reshape(I,...

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Is there a way to vectorise this vector/matrix product?
G = real(dot(W,R*W,1)).';

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Relative Ranking of position in an array
I10=[1 2 1 1 1 2 1 1 2 2 1 3 6 3 1 3 3 1 4 3 4 3 2 3 4 2 3 3 4 2 7 4 6 2 5 4 5 5 5 5 6 7 5 4 5 8 8 6 4 5 4 6 6 7 9 7 7 2 7...

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Optimize repeated permutation of a large vector
s = [1 2 3 4 5 6 7 8]; n=[4 3 1]; c=cumsum([0 n]); p=2:length(s)+1; p(c(2:end))=c(1:end-1)+1; s(p)

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Error using fwrite : Cannot write value: sparse arrays are unsupported.
[i,j,v] = find(S); then save i,j,v with fwrite

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Optimize repeated permutation of a large vector
s = [1 2 3 4 5 6 7 8]; i=1:length(s); n=[4 3 1]; c=cumsum([1 n]); b=cumsum(ismember(i,c)); p=mod(i+1-c(b),n(b))+c(b) s(p...

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find the position of all non-zero minimum values in each column of a matrix
a = [2 0 3;1 2 5;0 0 0;1 3 3;0 0 6;0 2 7;1 0 0] b=a; b(b==0)=NaN; [r,c]=find(b==min(b,[],1)); rmin=accumarray(c(:),r(:),[siz...

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Turn logical matrix into string vector
Assuming idx has one 1 per row idx = logical([0 1 0; 0 0 1; 1 0 0; 1 0 0; 0 1 0]); vec = ["A","B","C"]; [r,c]=find(idx); r...

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Symetric matrix power optimization
Youeu can edit MATLAB function mpower.m and try to the basic calculation (line 76 in my case) D = D*D; % I assume p is integer...

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How can I avoid loop for code optimization?
Use MultipleQR FEX (C compiler for MEX build is required, unless for Windows platform) y = linspace(1,10,1000); Y = reshape(...

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random number of two random varibles.
If K is the (2 x 2) covariariance matrix of (w,T) and mu (2 x 1) is the mean of (w,T), you can generate them like this n = 100...

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How to avoid a negative solution with fmincon, including an external equation?
The condition f2 = - 2*x1 - 10*x2 + 30 >= 0 is equivalen to 2*x1 + 10*x2 + 0*f1 <= 30. So set A = [2 10 0] b = 30 If you ...

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How can I optimize coefficients of a polynomial using fmincon?
"The overall goal is to minimize the length of the cost function " The overall length is L = integral sqrt(dx/dt^2+dy/dt^2+dy/...

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Is it possible to vectorize this?
NOTE the order of most is sorted with this algorithm: A = [1 2 0 3 4 6; 9 3 4 0 9 5; 4 3 0 5 6 7; 3 7 7 3 0 0...

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Diagonal of non-square matrix
n = 8; A = spdiags([2 3 4]+zeros(n,1),0:2,n,n+2); A = full(A) % if prefered

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Randomly splitting of a number in a sum format.
This code will generate "uniform" partition distribution, in the sense that all possible partition has equal probability: n = 1...

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Will codegen accelerate sub-functions?
Yes coder translates the sub-functions to C as well.

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Randomly splitting of a number in a sum format.
n = 10; for j=1:10 r = n; i = 1; clear s while r > 0 s(i) = ceil(r*rand); r = r-s(i); ...

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mldivide algorithm for an underdetermined system of equations
The outline of "\" goes as following: % Test data A=randi(10,3,2)*randi(10,2,5) b=randi(10,3,1) [Q, R, P] = qr(A,'vector')...

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Function to create struct with parameters
s = buildparams() function s = buildparams() a = 1; b = 2; s = gathervars(); end function s = gathervars() vars = eva...

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nchoosek_enum
nchoosek with enumerate selection. This function never build the full combination array in memory

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Creating separate combinations with repetition
I program a function nchoosek_enum that is almost like nchoosek, excepted that you can pass an enumerated array i that selects t...

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How to get all combinations from this matrix?
ch=['MRWI' 'IDMZ' 'CGBI' 'JKNO']; c=num2cell(ch,2); [c{:}]=ndgrid(c{:}); n=size(c,1); c = reshape(cat(n+1,c{:}),[],n)

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How to trim the non-manifold triangle off the stl file?
There is SW that can detect topology issue and attempt to correct it, such as https://www.meshlab.net/

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how to count the number of occurrences of these numbers (with some conditions)
A(1,:) = [1, 2, 5, 2 , 1 , 2]; A(2,:) = [0,1,1,0,1,0]; [B,~,J] = unique(A(1,:)); N = accumarray(J(:),A(2,:)'); B = B'; ta...

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How to select complementary elements from a vector?
d = [33 20 4 5 6 75 8 9 0]; I = [1 3 7]; d(I) = []

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How to select complementary elements from a vector?
d = [33 20 4 5 6 75 8 9 0]; I = [1 3 7]; d(setdiff(1:end,I))

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