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# Fabio Freschi

### Politecnico di Torino

201 total contributions since 2014

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How to change a column vector into a square a matrix?
Not as elegant as it could be but it works, especially for small matrices % matrix dimension n = 3; % your entries (here du...

11 days ago | 0

Calculate acceleration from velocity and time fron excel
acceleration = diff(data.Velocity)./diff(data.Time); Note that this vector has one entry less than the original ones, so you ma...

1 month ago | 0

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Subscripted assignment dimension mismatch.
You can use repmat and create a char array function bigstring = string_multiplication(str,N) bigstring = repmat(str,N,1); ...

2 months ago | 0

Simulation errors when multiplying matrices
I start a new clean answer You don't have to use the index i inside your matrix like you are doing in your code: in that way yo...

3 months ago | 0

Solving Complex Matrix Operations
You can do this in a for loop or using arrayfun % your A vector A = rand(1,1001); % dummy vector % calculation of the matr...

3 months ago | 0

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Replicate values in a matrix i-1 times
Quick and dirty for loop A=[1; 4; 8; 3; 2; 6] B = []; for i = 1:length(A) B = [B; repmat(A(i),i,1)]; end You can als...

3 months ago | 0

Find independent variables that minimize function
If you have only lower and upper bounds, use them directly in fmincon % your function fun = @(x) ((x(1)-real(0.5*(x(1)-(sqrt(x...

3 months ago | 0

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Simulation errors when multiplying matrices
Inside the loop in the first instruction Vn(:,i) is 5x1 but T is 5x5. Matlab now (starting in 2016, I guess) implicitly expands ...

3 months ago | 0

Weighted fit using fmincon
How about to repeat the samples of the points you want to weight more?

3 months ago | 0

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how to find the optimal value of a matrix that minimize a function?
If I understand correctly the problem can be recast to the following A*W = B*H = F; [a11 a12; a21 a22]*[w1 w2 0 0; 0 0 w3 w4] ...

3 months ago | 0

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plot 2 3D vectors in Matlab
% vectors a = [1 2 -3]; b = [-3 12 -13]; % starting point C0 = [0 0 0]; % put vector in a matrix, to make the code more...

3 months ago | 0

Error using sparse Index into matrix must be positive.
Simply remove "-1" from the definition of R. randi returns pseudorandom integers between 1 and the first inupt. The entries of C...

3 months ago | 0

How to solve time and space deriavtive using ode45?
Have a look at pdepe: it solves 1-D parabolic and elliptic PDEs

3 months ago | 0

Finite Difference Matrix Help
Edit: I changed my answer including a reference and the second order derivative The coefficients for central differences of dif...

3 months ago | 0

improved Euler integration scheme (possible code error) in matlab
I think it should be "-" p(1) = (-z(1)*(1-(z(2)))); p(2) = z(2)*(1-(z(1)));

3 months ago | 0

Make entries of first row and column of matrix all equal to zero.
% nullify first col B(:,1) = 0; %nullify first row B(1,:) = 0;

4 months ago | 0

plot vector using complex numbers
You can use compass or quiver % your matrix A = [-3+4i;-2+5i;1+3i;6+2i;-1-8i]; % with compass figure compass(real(A),imag...

5 months ago | 0

constantly receiving an error undefined function or variable z when use solve
Polynomials with a degree greater than 4 do not have explicit solutions. You can use vpa syms x y f1 = y == x^3 f2 = x^2+y^2...

5 months ago | 0

How to multiply only some column and rows for a given number?!
You are close to the answer, but you need to keep the first column % your matrix with data A = rand(2,21); % multiply all b...

5 months ago | 1

Unstable derivative approximation when steps get too small
This is expected. Look here for details https://blogs.mathworks.com/cleve/2013/10/14/complex-step-differentiation/

5 months ago | 1

How to start streamlines on the surface of a sphere? griddedInterpolant requires at least two sample points in each dimension
It looks like streamline does not accepts coordinates coming from your spherical construction. If you start form a cartesian gri...

5 months ago | 2

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n! permutation matrices
Is this what you wish? % identity matrix A = eye(4); % permuatations idx = perms(1:4); % all matrices in a cell array B = ...

6 months ago | 0

Solve the system of the 1-st order differential equations
Have a look at the ode suite

6 months ago | 0

How to make two vectors the same size?
Try fkld=sum(dot(p,log(p./q))); with the element-wise division ./

6 months ago | 1

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Inner matrix dimensions must agree
fkj= sum(.5*((p.^2-q.^2).^2)./((p.*q).^1.5)); Note that .^ .* and ./ operators are used for element-wise operation (see also St...

6 months ago | 1

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Inverse matrix in Matlab very different to Excel
The answer is not very different. As Jeremy commented, the results are similar a part from numerical tolerances. You can verify ...

6 months ago | 1

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How to call a multi output function without repeating the run
function [c, ceq] = nonconst(x) [total_value, Delta_value, energy_value] = digital(x); c = total_value-u*v;... ` `%fi...

6 months ago | 0

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How to color a mesh by temperature(or other value) preserving the elevation. Using two matrix(same length)
% dummy data [X,Y] = meshgrid(1:0.5:10,1:20); Z = sin(X).*cos(Y); T = X+Y; % plot surf(X,Y,Z,T) colormap('hot') colorba...

6 months ago | 1

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How can I get an array of velocity if I have an array of position and another array of time
First, you need a element-wise division pos = [0 2 4 8 16 32 64]; t = [0 0.1 0.2 0.3 0.4 0.5 0.6]; V = diff(pos)./diff(t); ...

6 months ago | 0

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