Heat transfer problem using runge kutta 4 method. Error in function

function [ du ] = du( r,T ) %UNTITLED5 Summary of this function goes here % Detailed explanation goes here dr=0.005; ri=0.05; ro=0.075; rm=0.62; r=(ri:dr:ro); T(1)=700; taui=4.9; tauo=5;

if r<rm; du=(taui./(dynamic_viscosity+density.*epsilonm)).*((rm.^2)-(r.^2)./((rm.^2)-(ri.^2)))*((ri./r));

else du=-(tauo./(dynamic_viscosity+density.*epsilonm).*((r.^2)-(rm.^2))./((ro.^2)-((rm.^2))*(ro./r)));

end

Error in du (line 14) du=(taui./(dynamic_viscosity+density.*epsilonm)).*((rm.^2)-(r.^2)./((rm.^2)-(ri.^2)))*((ri./r));

when i try to run it, an error appears that there is an undefined function 'r'.

[Chris C]

How are you calling this function? Are you using a built in ODE solver (i.e. ode45, etc.) or are you building your own RK4 method?

Maybe you can give a little more detailed explanation of your system (heat system). That would help me to disect your code and find out what's going on.

[Sagar Damle]

Richard,to separate code part of your question from other stuff,after copying the code,select it and use the provided button '{}Code'.