error is using bvpset in bvp4c

Hi, I am Syed,

I like to have an output with 6 or more than 6 decimal place (for example: 3.033334), without bvpset i am getting the output upto 4 decimal places, but i like to have upto to 6 or 8 decimal places, please guide me to get the desired output

The error i am getting is

Error using <=

Not enough input arguments.

My program is given below

close all

clc

phi=0.1;

phi1=2;

phi2=2;

Betaf=0.00021;

Betas=0.000058;

sigmaf=0.005;

sigmas=580000;

GR=2;

EM2=20;

Rof=997.1;

Ro=5;

c=0;

Ros=4420;

h=0.5;

Hc=0.25;

K=1;

R=1;

e1=(1./((1-phi).^2.5));

e2=(1-phi)+(phi.*(Ros./Rof));

e3=(1-phi)+phi.*((Ros.*Betas)./(Rof.*Betaf));

sigma=(sigmas./sigmaf);

e4=1-((3*(1-sigma).*phi)./((2+sigma)+(1-sigma).*phi));

gama1=e2./e1;

gama2=1/e1;

gama3=e3./e1;

s1=(e4./(phi1.*(1-i.*Hc)));

s2=(e4./(phi2.*(1-i.*Hc)));

dydx=@(x,y)[y(3);

y(4);

-EM2.*gama2.*y(4)+2.*i.*Ro.*gama1.*y(1)+gama3.*GR.*x+R.*gama1;

(-e4./(1-i.*Hc)).*y(3)];

BC = @(ya,yb)[ya(1);yb(1)-c;ya(4)-s1.*ya(2);yb(4)+s2.*yb(2)];

yinit = [0.01;0.01;0.01;0.01];

options = bvpset('stats','on','RelTol',le-3);

solint = bvpinit(linspace(0,1,50),yinit,options);

U1 = bvp4c(dydx,BC,solint);

dudy1=U1.y(3,1)

Answer 1

[Shashi Kiran]

Hi @Syed,

I understand that you are aiming to obtain an output with 6 or more decimal places but are encountering errors.

Here are my observations and corrections for your code:

• The error was because le-3 is not a valid expression. It should be 1e-3, which is the proper MATLAB syntax for .

options = bvpset('stats','on','RelTol',1e-3);

• The bvpinit function is used to initialize the solution guess and mesh, and it doesn't accept the options structure as an argument.

solint = bvpinit(linspace(0,1,50),yinit);

• The correct place to pass the options structure is in the bvp4c function call. This allows the solver to use the relative tolerance (RelTol) and print statistics ('stats', 'on').

U1 = bvp4c(dydx,BC,solint,options);

Here is the output following these corrections:

Refer to the following documentations for more details about the functions:

1. bvpset: https://www.mathworks.com/help/matlab/ref/bvpset.html
2. bvpinit: https://www.mathworks.com/help/matlab/ref/bvpinit.html
3. bvp4c: https://www.mathworks.com/help/matlab/ref/bvp4c.html

Hope this solves your query.

[Syed]

Thank you for your answer,

I tried the method you had instructed, but still i am getting 4 decimal places. The output i have shared for your reference.

options = bvpset('stats','on','RelTol',1e-3);

solint = bvpinit(linspace(0,1,50),yinit);

U1 = bvp4c(dydx,BC,solint,options);

The output is

The solution was obtained on a mesh of 50 points.

The maximum residual is 4.394e-05.

There were 499 calls to the ODE function.

There were 14 calls to the BC function.

The solution was obtained on a mesh of 50 points.

The maximum residual is 4.081e-05.

There were 499 calls to the ODE function.

There were 14 calls to the BC function.

The solution was obtained on a mesh of 50 points.

The maximum residual is 6.144e-05.

There were 499 calls to the ODE function.

There were 14 calls to the BC function.

dudy1 =

-0.3003 + 0.1168i

dudy2 =

-0.3062 + 0.1215i

dudy3 =

-0.3058 + 0.1212i

[Shashi Kiran]

Hi @Syed,

Use this at the start of your program for formatting your output to more decimal digits.

format long

[Shashi Kiran]

Additionally,

To set the default formatting for long in MATLAB, follow these steps:

- On the MATLAB homepage, go to Home.

- Navigate to Preferences.

- Under Command Window, select Text Display, then choose Numeric Format and set it to long.

[Syed]

I got it now, thanks a lot