Answered

Code for solving first-order ode with symbolic initial condition

syms y(h) k ode = diff(y) == k*y; sol_ode_general = dsolve(ode) vars = symvar(sol_ode_general) eqn1 = subs(sol_ode_general,v...

Code for solving first-order ode with symbolic initial condition

syms y(h) k ode = diff(y) == k*y; sol_ode_general = dsolve(ode) vars = symvar(sol_ode_general) eqn1 = subs(sol_ode_general,v...

5 days ago | 0

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Answered

How to convert PDE into matrix form

Can you write this in matrix form ? m1*diff(x1(t), t, t) + 0*m2*diff(x2(t), t, t) + (c1 + c2) * x1d - c2 * x2d + (k1 + k2) * x...

How to convert PDE into matrix form

Can you write this in matrix form ? m1*diff(x1(t), t, t) + 0*m2*diff(x2(t), t, t) + (c1 + c2) * x1d - c2 * x2d + (k1 + k2) * x...

5 days ago | 0

Answered

Why do I receive the error in horzcat?

blkdiag(ddf(x), zeros(n)) is 2x2, A' is 1x1. Thus it's not possible to concatenate the two horizontally in the command H...

Why do I receive the error in horzcat?

blkdiag(ddf(x), zeros(n)) is 2x2, A' is 1x1. Thus it's not possible to concatenate the two horizontally in the command H...

5 days ago | 0

Answered

Determine the coefficients in symbolic

I don't know why the coefficients appear in the wrong order. syms In In_1 On_1 On = 91/100*In-7/8*In_1+1/2*On_1; coeffs(On,[I...

Determine the coefficients in symbolic

I don't know why the coefficients appear in the wrong order. syms In In_1 On_1 On = 91/100*In-7/8*In_1+1/2*On_1; coeffs(On,[I...

6 days ago | 0

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Answered

how to solve non-linear equations in a nozzle

Maybe you can give better initial guesses in x0 for the solution than I can ... x0 = 10*rand(7,1); options = optimset('Max...

how to solve non-linear equations in a nozzle

Maybe you can give better initial guesses in x0 for the solution than I can ... x0 = 10*rand(7,1); options = optimset('Max...

6 days ago | 1

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Answered

Solving Nonlinear System of Equations with 10 variables

W=100; s=10; S=23; %F=13; %m=9; fun = @(X1,X2,X3,X4,X5,X6,X7,X8,X9,X10)... [5-(W+S*9)*X1+S*9*X2-S*20*X1^2+S*20*X...

Solving Nonlinear System of Equations with 10 variables

W=100; s=10; S=23; %F=13; %m=9; fun = @(X1,X2,X3,X4,X5,X6,X7,X8,X9,X10)... [5-(W+S*9)*X1+S*9*X2-S*20*X1^2+S*20*X...

6 days ago | 0

Answered

calculating Double integral over a region

syms x y int(int(2,y,-sqrt(1-(x/3)^2),sqrt(1-(x/3)^2)),x,-3,3)

calculating Double integral over a region

syms x y int(int(2,y,-sqrt(1-(x/3)^2),sqrt(1-(x/3)^2)),x,-3,3)

6 days ago | 1

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Answered

I am struggling to plot iteration vs error in the matlab code? can anyone help me with this? very much appreciate it.

% Inputs: A - Coefficient matrix A=[2 -1 0;-1 2 -1;0 -1 2]; % b - Input matrix b = [0; 2; 0]; % x0 - Initial guess x0 = [0...

I am struggling to plot iteration vs error in the matlab code? can anyone help me with this? very much appreciate it.

% Inputs: A - Coefficient matrix A=[2 -1 0;-1 2 -1;0 -1 2]; % b - Input matrix b = [0; 2; 0]; % x0 - Initial guess x0 = [0...

7 days ago | 0

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Answered

Is it possible to get a time-dependent function as an output of an ODE solver?

clear all clc I0= 500; % maximum flow Tc=60/72; % heart period Ts=(2/5*Tc); % time in systole P_ss=80; % diastolic p...

Is it possible to get a time-dependent function as an output of an ODE solver?

clear all clc I0= 500; % maximum flow Tc=60/72; % heart period Ts=(2/5*Tc); % time in systole P_ss=80; % diastolic p...

7 days ago | 0

Answered

Error in the script

x = -1 : 0.001 : 1; y_div = (x.^2) ./ (1 + (x.^2)); title ('División acotada'); plot (x, y_div);

Error in the script

x = -1 : 0.001 : 1; y_div = (x.^2) ./ (1 + (x.^2)); title ('División acotada'); plot (x, y_div);

7 days ago | 0

Answered

Reverse problem of finding time-varying parameters of an ODE with the help of solution data.

Use "lsqcurvefit" to fit the parameters together with an integrator (e.g. ODE45). For an example, see Star Strider's code under...

Reverse problem of finding time-varying parameters of an ODE with the help of solution data.

Use "lsqcurvefit" to fit the parameters together with an integrator (e.g. ODE45). For an example, see Star Strider's code under...

7 days ago | 1

Answered

im trying to solve a system of 4 nonlinear equations with 4 unknowns

Equations (1), (3) and (4) give x(2) = 0. Thus it's impossible to satisfy equation (2) where x(2) is in the denominator. syms x...

im trying to solve a system of 4 nonlinear equations with 4 unknowns

Equations (1), (3) and (4) give x(2) = 0. Thus it's impossible to satisfy equation (2) where x(2) is in the denominator. syms x...

7 days ago | 0

Answered

Corrective action after Newton iteration exception

I wonder if a similar corrrective action happens whenever a Newton-iteration exception occurs: in this case, does the solver sim...

Corrective action after Newton iteration exception

I wonder if a similar corrrective action happens whenever a Newton-iteration exception occurs: in this case, does the solver sim...

7 days ago | 0

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Answered

The size of X must match the size of Z or the number of columns of Z.

Change dx = 1.01/(Nx-1); dy = 1.01/(Ny-1); to dx = 1.0/(Nx-1); dy = 1.0/(Ny-1);

The size of X must match the size of Z or the number of columns of Z.

Change dx = 1.01/(Nx-1); dy = 1.01/(Ny-1); to dx = 1.0/(Nx-1); dy = 1.0/(Ny-1);

7 days ago | 0

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Answered

Why should I tighten error tolerances if I am violating minimum stepsize?

The stepsize reduction down to the minimum stepsize often occurs because in previous time steps, the solver was not exact enough...

Why should I tighten error tolerances if I am violating minimum stepsize?

The stepsize reduction down to the minimum stepsize often occurs because in previous time steps, the solver was not exact enough...

7 days ago | 0

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Answered

Num2cell question

Most probably too large for your computer: A = rand(12,3,5) A = num2cell(A)

Num2cell question

Most probably too large for your computer: A = rand(12,3,5) A = num2cell(A)

7 days ago | 0

Answered

Matlab produces complex number where it cannot be produced

Because (Req.^3-b.*Req.^3)/(R.^3-b.*Req.^3) is negative. If you use k1 = 4; k2 = 1/3; P0=1.00*10^5; Req=69.2*10^(-3); b=...

Matlab produces complex number where it cannot be produced

Because (Req.^3-b.*Req.^3)/(R.^3-b.*Req.^3) is negative. If you use k1 = 4; k2 = 1/3; P0=1.00*10^5; Req=69.2*10^(-3); b=...

7 days ago | 1

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Answered

Help with fminsearch to maximise non-analytic function via specific parameters

Here is the optimization solution: theta0 = 10; sol = fminsearch(@fun,theta0) function range = fun(theta) global rho d m g...

Help with fminsearch to maximise non-analytic function via specific parameters

Here is the optimization solution: theta0 = 10; sol = fminsearch(@fun,theta0) function range = fun(theta) global rho d m g...

8 days ago | 0

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Answered

Why are the inputs to the functions used in the ODE45 solver not in the right syntax?

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %This is in thé main script: field = [1,0,1 ; 1,1,1]; %in my script ...

Why are the inputs to the functions used in the ODE45 solver not in the right syntax?

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %This is in thé main script: field = [1,0,1 ; 1,1,1]; %in my script ...

8 days ago | 0

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Answered

2nd order differential eqn for Windkessel model

I = @(t) I0*sin((pi*t)/Ts).^2.*(t<=Ts); %input current flow Idot = @(t) I0*2*sin(pi*t/Ts).*cos(pi*t/Ts)*pi/Ts.*(t<=Ts); Idotdo...

2nd order differential eqn for Windkessel model

I = @(t) I0*sin((pi*t)/Ts).^2.*(t<=Ts); %input current flow Idot = @(t) I0*2*sin(pi*t/Ts).*cos(pi*t/Ts)*pi/Ts.*(t<=Ts); Idotdo...

8 days ago | 0

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Answered

Help with fminsearch to maximise non-analytic function via specific parameters

Of course, you could use fminsearch for optimization. But using it, you will only get a single point of the below graph. Theta ...

Help with fminsearch to maximise non-analytic function via specific parameters

Of course, you could use fminsearch for optimization. But using it, you will only get a single point of the below graph. Theta ...

8 days ago | 0

Answered

What type of solver is VPA Solve?

https://de.mathworks.com/matlabcentral/answers/298048-which-algorithm-does-vpasolve-use

What type of solver is VPA Solve?

https://de.mathworks.com/matlabcentral/answers/298048-which-algorithm-does-vpasolve-use

8 days ago | 1

Answered

"Error using indexing Not enough inputs to inline function; Error in NRM (line 93) INJAC=JAC(x1,x2)" showing in a multivariable Newton Raphson program.

For the 3-variable case, the line INJAC=JAC(x1,x2); has to be changed to INJAC=JAC(x1,x2,x3);

"Error using indexing Not enough inputs to inline function; Error in NRM (line 93) INJAC=JAC(x1,x2)" showing in a multivariable Newton Raphson program.

For the 3-variable case, the line INJAC=JAC(x1,x2); has to be changed to INJAC=JAC(x1,x2,x3);

8 days ago | 0

Answered

Im trying to use gradient decent with a for loop to determine the value of x that minimizes the function

f = @(x) x.^2 - 3*x + 1; iterations = 15; alpha = 0.15; x = zeros(iterations,1); x(1) = 0; for...

Im trying to use gradient decent with a for loop to determine the value of x that minimizes the function

f = @(x) x.^2 - 3*x + 1; iterations = 15; alpha = 0.15; x = zeros(iterations,1); x(1) = 0; for...

8 days ago | 0

Answered

RK4 method to solve a 2nd ODE.

The definition of the function handles f1 and f2 is wrong: f1 = @(u,z,t) z0; % Initial f1 f2 = @(u,z,t) A*z0(t)+B*u0...

RK4 method to solve a 2nd ODE.

The definition of the function handles f1 and f2 is wrong: f1 = @(u,z,t) z0; % Initial f1 f2 = @(u,z,t) A*z0(t)+B*u0...

8 days ago | 1

Answered

the code is so slow , ode23, what can I do get it faster

B1 = [0.007664184 -2.9881 0.000406092 0.1383288248 10 0.0053322412 -3.048 0.0002825517 0.0714132532 12 0.0042969663 -3...

the code is so slow , ode23, what can I do get it faster

B1 = [0.007664184 -2.9881 0.000406092 0.1383288248 10 0.0053322412 -3.048 0.0002825517 0.0714132532 12 0.0042969663 -3...

8 days ago | 0

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Answered

How to calculate u for every alpha?

... f= @(x)(0*zeros(size(x))); alpha = [2,5,10,15,20]; %lineare Basisfunktion A = assemDiffusion1D(nodes, epsilon); b = ass...

How to calculate u for every alpha?

... f= @(x)(0*zeros(size(x))); alpha = [2,5,10,15,20]; %lineare Basisfunktion A = assemDiffusion1D(nodes, epsilon); b = ass...

8 days ago | 0

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Answered

Using least square fitting function lsqr

rng(0) n = 20; s = rand(1, n) > 0.5; s = repmat(s', 1, 100)'; s = s(:)'; t = linspace(0, n, numel(s)); subplot(2, 1, 1) p...

Using least square fitting function lsqr

rng(0) n = 20; s = rand(1, n) > 0.5; s = repmat(s', 1, 100)'; s = s(:)'; t = linspace(0, n, numel(s)); subplot(2, 1, 1) p...

8 days ago | 1

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Answered

Code optimization by way of selective computations

Ts = 1e-7; t = 0:Ts:1-Ts; tic s_t = exp(1i*2*pi*t(1:2:end)); toc or if your condition is more complicated: tic s_t = exp(1...

Code optimization by way of selective computations

Ts = 1e-7; t = 0:Ts:1-Ts; tic s_t = exp(1i*2*pi*t(1:2:end)); toc or if your condition is more complicated: tic s_t = exp(1...

8 days ago | 0

Answered

how to combine to get single graph in optimal control problems

Use "hold on" and "hold off" to plot several graphs in one figure: f = @(x) x.^2; g = @(x)sqrt(x); x = 0:0.01:1; hold on pl...

how to combine to get single graph in optimal control problems

Use "hold on" and "hold off" to plot several graphs in one figure: f = @(x) x.^2; g = @(x)sqrt(x); x = 0:0.01:1; hold on pl...

8 days ago | 0