diffusion of liquid using ode45

Hi...good gracious!

I am new using ode45. I have to represent diffusion of a drug in a solution (dC/dx) using ode45, where C is the concentration of drug and x is the distance from the boundary. The concentration of drug (c) decreases with increase in distance(x). The only know information i have is that the initial concentration of drug is C0=500 ml at x=0, and at a distance x=12 the concentration of drug is C0/7. Please help me to reprent and find the solution and plotting using ode45.

[Milan Chavda]

Your problem seems to be more likely of a boundary value problem and not the Initital value problem, I would suggest to use bvp4c command or a numerical method for the same.

Kindly have a look at the below links and adjust your equation and parameters accordingly, I hope that would fix it.

https://in.mathworks.com/help/matlab/math/boundary-value-problems.html

https://in.mathworks.com/matlabcentral/fileexchange/71361-finite-difference-explicit-method-for-fick-s-2nd-law

[Dhruba jyoti Bora]

Thank u sir for your reply. Definitely i will look into the boundary value problem. However how to solve it, in case if we retain the initial value condition only for this problem? Thank u for the link. this is infact Fick's first law of diffusion.

[J. Alex Lee]

Do you want to solve the steady problem or transient problem? From context it appears you want the transient problem, tracking the concentration profile from an initial "spike". If so, ode45 is an appropriate function for your workhorse, provided that you manually discretize your spatial profile (such as by finite difference). Alternatively, look into pdepe.

Before you consider how to solve, you need to decide the equations to solve...are you doing this in a planar geometry ( a flat plane spiked with drug), cylindrical geometry (straight line of drug), or spherical geometry (a spot of drug)?