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# Vladimir Sovkov

### St. Petersburg State University

74 total contributions since 2014

Professional Interests: computational physics, applied mathematics

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Answered
Issue with 'for' loop - trying to iterate through and change certain values to 0 in array
If the equality must be exact, just x_results(x_results==.3095)=0; and nothing else (sometimes can produce an incorrect result...

26 days ago | 0

Answered
How can I create a script that calculates this combinatorial?
C=nchoosek(n,r)

27 days ago | 0

Answered
Specify eigenvector for eigs
Matlab documentation: 'StartVector' — Initial starting vector random vector (default) | vector Initial starting vector, spe...

28 days ago | 0

Answered
How to "wrap text" on pushbutton string?
Use the cell array with entries containing text fragments to be shown in separate strings.

1 month ago | 0

Answered
how to implement the algorithm for approximating Cosine using the Taylor series
syms theta n=4; taylor(cos(theta),'Order',n)

1 month ago | 0

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Submitted

aux2bib
BibTex (LaTeX) sublibrary from an AUX file

2 months ago | 0 downloads |

Answered
Is there any way to accelerate the solving of a series of large sparse positive definite linear equations "Ax=b" with same "A" and different "b"?
It depends... Besides inv(A), you can try A\eye(n), pinv(A)--all of them are equivalent for a well-conditioned A and different ...

2 months ago | 0

Answered
Is there any method to calculate the inverse of matrix which changed a few values?
I am not sure how much profitable it is numerically, but the Sherman Morrison theorem can be a way, see https://en.wikipedia.org...

2 months ago | 1

Answered
What does ''all'' mean in M = min(A, []. ''all'') ?
All this is fairly well described in the matlab documentation. min(min(A)) and min(A, [], ''all'') are equivalent for 1D and 2D ...

2 months ago | 0

Answered
If I have multiple function, then how can I get the function of min(fun1,fun2,fun3,...)?
xmin=min([R1(x(:)');R2(x(:)');...]); % to get a correct result, the argument must be a row-vector: x(:)' turns any input array t...

2 months ago | 0

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Answered
Is there a bug in the if function
This is not a bug in the if function but an artefact of the rounding of the matlab bit-wise arithmetics. To avoid this effect, s...

2 months ago | 0

Answered
Angle between two lines in frontal plane
If, as it looks in the figure, (...Y) are the verticle coordinates and (...Z) are the horizontal coordinates, then the basic geo...

2 months ago | 1

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Answered
solve function give a wrong solution
syms x solv = double(solve( (1+x/12)^12 == 1.02)) There are many solutions. The one you are interested in is rather 0.01981897...

2 months ago | 0

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Answered
How to see the current value of the variable in "fminsearch" optimization?
optimset('Display','iter'); From Matlab documentation: 'Display' — Level of display 'notify' (default) | 'final' | 'off' | 'n...

2 months ago | 0

Answered
showing the distance between the two plots on two curves at regular intervals on the same plot
t=0:0.2:10; % avoid loops wherenever possible, use element-wise operations instead x=t.^2; y=0.5*x+10; % the same as "y=0.5*t...

2 months ago | 0

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Answered
Writing into .txt file
T = [v angle_random]; % this is if you want a 2-column file save('random_cylind.txt','T','-ascii','-double'); % explore availab...

2 months ago | 0

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Answered
Debugging using external editor
https://www.mathworks.com/help/matlab/matlab_external/debugging-on-microsoft-windows-platforms.html

2 months ago | 0

Submitted

aux2bib
BibTex sublibrary from a LaTeX AUX file

2 months ago | 0 downloads |

Answered
How do I record the location of a specific value in a set of data?
a=[0 0 0 0 1 0 1 0 0]; k=find(a==1,1)

3 months ago | 0

Answered
How to Convert 3d matrix to row matrix???
a=rand(2,2,2) % a sample 3D matrix a b=a(:)' % is turned to the 1D row matrix b

5 months ago | 2

Answered
Plot the trapeoidal waveform using given equations
syms theta y=piecewise(... 0<=theta<2*pi/3,1,... 2*pi/3<=theta<pi,(1-6/pi*(theta-2*pi/3)),... pi<=theta<5*pi/3,-...

7 months ago | 0

Answered
How to draw an ellipse
The code discussed at https://www.mathworks.com/matlabcentral/answers/497966-how-to-find-the-vertical-height-of-an-ellipse-y-axi...

7 months ago | 0

Answered
Eigenvalues corresponds to eigenvectors
Absolutely standard: L(k,k) ~ V(:,k). You can check it with the code: for k=1:size(h,1) disp(strcat('k=',num2str(k),'; h*v-la...

7 months ago | 0

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Answered
Subs Command for Multivariable Function
If e^ is the exponent and if you want to estimate the result numerically (from the question it is not quite clear what you want)...

7 months ago | 0

Answered
Partial least-squares regression evalutaion
The equation considered in PLS of Matlab is rather Y = X(:,:)*B(2:end,:) + repmat( B(1,:),n,1 ) + E, where: X is an n-by-...

8 months ago | 0

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Answered
Normalization of complex eigenvector
You probably want V(:,1) = V(:,1)/norm(V(:,1)); Besides, if your theta and phi are supposed to be real, the overall computatio...

8 months ago | 0

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Answered
Eigenvector without calling eigenvalues
This is not an error but a warning that you do not use the eigenvalues, which influences nothing. If you want to avoid it, subst...

8 months ago | 0

Answered
Can I check if factored and expanded polynomial forms are equal?
simplify((w^2-k^2) - (w+k)*(w-k)) ans = 0 expand((w+k)*(w-k)) ans = w^2 - k^2 factor(w^2-k^2) ans = [ -1, k - w...

8 months ago | 0

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Answered
How to call some object handle from opening function of figure?
u0=findobj('Tag','lst1','Style','listbox','Parent',gcf); % search for all the object properties you used to identify it set(u0,...

8 months ago | 0

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Submitted

Wigner 3j-6j-9j
Wigner 3j-, 6j-, 9j-symbols

8 months ago | 5 downloads |

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