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# Fabio Freschi

### Politecnico di Torino

191 total contributions since 2014

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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...

4 days 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...

4 days ago | 0

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

4 days 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...

5 days 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)));

5 days 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;

1 month 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...

2 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...

2 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...

2 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/

2 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...

2 months ago | 1

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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 = ...

3 months ago | 0

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

3 months ago | 0

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

3 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...

3 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 ...

3 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...

3 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...

3 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); ...

3 months ago | 0

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Numerical Solution for a System of THREE Differential Equations
This is an ODE, not PDE. Look for the ODE suite

3 months ago | 0

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Area under curves with different length (trapz)
If you have the x axes for both waves, it is pretty easy to use trapz: N1 = 1036; N2 = 9958; % wave 1 x1 = linspace(0,2*pi...

3 months ago | 1

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Plotting the integral of a graph
Suppose that x and y are the vectors defining your waveform. % dummy values x = linspace(0,2*pi,1000); y = sin(x); % integ...

3 months ago | 1

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Does anybody know how to write a function which returns the coordinates of a convex hull of a list of certain points?
% your data N = 20; List = rand(N,2); % convex hull (k is the pointer to the rows in List with the convex hull k = convhul...

3 months ago | 0

How to divide a part of array to the another part of it?
T = psi2(1:5)./psi(end-4:end);

3 months ago | 0

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How can speed up the blow codes?
Edit: added attempt for ncount I don't understand what ncount is doing, it looks like a counter but I don't understand why you ...

3 months ago | 0

defined n with the equation
n= size(P4,1)

3 months ago | 0

Array indices must be positive integers or logical values
Your index k starts from 0 and you are indexing h with k, so you are asking at the first iteration h(0). Matlab has 1-indexing s...

3 months ago | 0

while loop performance improvement
I don't know the starting value of k, assuming it is 1 idx = 1:rate:period mysum = sum(array(idx,2)); % note that sum is the n...

3 months ago | 1

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Euler method error in code Index exceeds the number of array elements (1). in my my code
Checking the sintax of the code only I see 3 issues 1) In the for loop you wrote a(400-x(n)), that is you are addressing the po...

3 months ago | 1

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