# Alan Stevens

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**Content Feed**

Phase Portrait of ODE system

Do you mean something like this: % Part IIa. Base Case % Phase Portrait % % r=2.5; p=2; c=0.1; b=0.1; % % [x,v]=meshgr...

7 days ago | 0

Plot with while loop

By the time you get to the plot command you only have a single value of t1 and a single value of y1 as you overwrite each of the...

15 days ago | 0

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How should I approach solving differential equation as function of two variables r, k?

You need to call the ode with something like [t, y] = ode45(@(t,y) deq(t,y,r,k),tVec,y0,r,k); where you pass values of r and k...

17 days ago | 1

I need help plotting

More like this perhaps: Z1=500; Z2=50; Z3=500; u=1; tau1=(2*Z2)/(Z1+Z2); tau2=(2*Z1)/(Z1+Z2); tau3=(2*Z3)/(Z3+Z2); p1=(Z...

27 days ago | 1

1D Heat Equation Explicit Scheme

Look at for i=1:(N) if (alpha*DELTA_t)/(DELTA_x^2)<=0.5 T(i,j+1)=T(i,j)+((alpha*DELTA_t)/((DELTA_x)^2))*(...

28 days ago | 1

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Solving a system of Second Order Equations

Not sure there is a symbolic solution, but it's easy enough to get a numerical one: tspan = [0 1]; % Start and end times % In...

29 days ago | 1

How to solve 4th order Runge-Kutta for different initial conditions?

Here's a rather crude method (together with some corrections). You should be able to turn this into a much more elegant version...

1 month ago | 1

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1D Heat Equation Explicit Scheme (fixed)

With for i=0:0.1:50 you are trying to index variables with zero. However, Matlab's indexing starts at 1.

1 month ago | 1

How to plot Homogeneous solution and Particular integral seperately of a second order differntial equation using ode45

ode45 just solves first order equations, so turn your second order equation into two first order ones, like so: y' = v v' = -4...

1 month ago | 0

Trying to plot R_K 4th order, but keep getting straight line?

Check these equations F_sir = @(s,i,r) -a*s*i; % change the function as you desire G_sir = @(...

1 month ago | 1

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Not enough input arguments; fzero function

Replace T_mix = fzero(fun,T_mix_0); by T_mix = fzero(@fun,T_mix_0);

1 month ago | 1

I am trying to use the trapezoidal rule to compute the flow rate of fluid through a pipe.

I think it needs to be more like this: % Velocity distribution function of the pipe % Area = pi*r^2 % dA = 2*pi*r dr % Q = V...

1 month ago | 0

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How to get area under the fit attained by Curve Fitting tool?

Try help trapz

1 month ago | 0

Progressively slower performance and task constraints using matrix and loops

With these particular functions it's easy to precalculate the Jacobian function and do everything numerically (and quickly). Fo...

1 month ago | 0

Local Stiffness Matrix Negative

How about replacing if i==2 & j==2 k=A(e)*E/(L/5); elseif i==2 & j==1 k=...

1 month ago | 0

Save array values in a for loop

Try replacing error = max(abs(double(y1-z1(vx)))) with error(i) = max(abs(double(y1-z1(vx))));

1 month ago | 0

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Solving a PDE with two variables using cank nicolson method

Matlab indices start at 1, so the loops i, j and K in the following for i=0:N for j=0:M for K=0:1 f(x,y...

2 months ago | 0

Solving a System of 2nd Order Nonlinear ODEs

You haven't passed y and z to the funcion in function dydt=mbd(M,m,g,lc,k) Probably needs to be more like function dydt=mbd(t...

2 months ago | 0

Can I comment only a section or part of a line?

Like this: x = linspace(0,2*pi,100); y1 = sin(x); y2 = cos(x); plot(x,y1,... % comment x,y2)

2 months ago | 0

Adding subtitle to the plot

In Matlab 2018 try title({'Main title text';'subtitle text'}) (Note the curly brackets)

2 months ago | 0

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Left-rotating a vector

You define B as a null vector so it doesn't have an "end". Try, simply A = [1,2,3,4,5]; B = [A(2:end) A(1)]

2 months ago | 0

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How can I solve this error : Invalid text character. Check for unsupported symbol, invisible character, or pasting of non-ASCII characters.

This works for me: n=input('donner le nombre de points: '); k=0; for i=1:n u1=rand;u2=rand; x=2*u1; y=2*u2...

2 months ago | 0

Lax-Wendroff method for advection equation with periodic boundary condition

If you make dt=0.1*h/a; instead of dt=0.95*h/a; your max error reduces to 0.0355.

2 months ago | 0

I want to solve the unknown variable t1

Well, this gets it working, though who knows if it makes any sense!" A0 =500; D0=100; c1=5; c2=10; c3=10; c4=8; a=30; a2...

2 months ago | 0

How to make convergence plot (error VS time step) in a log-log scale among four numerical methods and exact solution?

This should give you the right idea: %% 1st-order Adams-Bashforh Solution fun = @(t,y) (y); %Function f(t,y) y0 = 1; %Initial...

3 months ago | 0

i need some help with finding the damping ratio

Use fzero: x = [12.73, 25.36, 37.99]; y = [0.77, 0.29, 0.11]/2; zeta = fzero(@(zeta) fn(zeta,y),0.5); disp(['zeta = ' nu...

3 months ago | 0

How to make graph that plot between Analytical Solution (Exact Solution) and Numerical Method Solution?

After Y = exactY(t2) you probably need something like: plot(t2,Y2,t2,Y) legend('AM','Exact') However, you haven't supplied th...

3 months ago | 0

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How to numerically solve and plot definite integral with variable upper limit

Like so: K= @(t) (sin(t)-t.*cos(t)).*sin(t); P = 0:0.1:3.1416; for i = 1:numel(P) V(i) = integral(K,0,P(i)); ...

3 months ago | 0

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merge two matrices after odd rows

Here's one way: A=[1 1;1 1;1 1]; B=[2 3;4 5;6 7]; AB = [A B]'; C = reshape(AB,2,6)'

3 months ago | 0

Hello, I am trying to solve the ODE but I have an error I do not understand how to solve. Would appreciate some help. Thank you!

Like this? %% ODE45_estimation % ------ Constants ------ % m = 1248.5; g = 9.81; W = m*g; S = 17.1; % ------ Time int...

3 months ago | 0