Problem with initial condition

When I run ode I get the eerror message "@(X,G)FLUX_DIM(C,RHO_FUEL,A,RHO,X,G) returns a vector of length 100, but the length of initial conditions vector

is 300. The vector returned by @(X,G)FLUX_DIM(C,RHO_FUEL,A,RHO,X,G) and the initial conditions vector must have

the same number of elements.

Np =300;
x=linspace(0,L_grain,Np) ;
x=x(:);
x_0=zeros(1,Np);
x_0=x_0(:);

[x_sol,G_sol]=ode45(@(x,G)flux_dim(C,rho_fuel,A,rho,x,G),[0,L_grain],x_0);

function DG_dx=flux_dim(x,A,rho,C,rho_fuel,G)


DG_dx=(-C-A).'.*(rho-rho_fuel);

DG_dx=DG_dx(:);

end

[Walter Roberson]

@(x,G)flux_dim(C,rho_fuel,A,rho,x,G)

That is how you are calling the function

function DG_dx=flux_dim(x,A,rho,C,rho_fuel,G)

That is how you are declaring the function. Notice the different order of parameters.

[Francesco Renzulli]

I have tried to change this but it gives always the same error message

[Mathieu NOE]

tried to run your code but many constants are missing

even thougt x and G are in the function args they are not used in the DE

[Francesco Renzulli]

I know i didn't pubblish all the code because it is long, maybe the problem is rho, that is a solution fromm another ODE45

Answer 1

[Aditya Shah]

Hi!

The problem seems to have occurred due to a mismatch between the size of the output vector of the function FLUX_DIM and the size of the initial conditions vector.

I am assuming the size of the following variable as:

C: 1x100

A: 1x100

rho: 100x1

rho_fuel: scalar

Correcting the size of initial condition by changing the value of variable Np to 100, solves the problem.

Please note the size of variable was referred from the following Matlab Answer post:

https://www.mathworks.com/matlabcentral/answers/710553-problem-with-matrix-dimension