how can I write c,f,s in pde function?

if c is changing with x then how to write f and s

function [c,f,s]= pdefun1(x,z,u,DuDx)
c = (2*U_a/D_s)*(1-x.^2/R1^2);       %%% HERE c is changing with x
f = DuDx; 
s=0;
end
%%
function u0 = pdeic1(x)
u0 =20;
end

%%
function [pl,ql,pr,qr] = pdebc1(xl,ul,xr,ur,z)
 
pl=0;
ql=1;
pr=0.6*u0;  
qr=1;
end

[Torsten]

Why should it affect f and s if c is changing with x ?

[Shangeetha Mahendran]

Thank you for the reply.

I thought i have to give c in vector format, therefore, s,f should be in vector format.

[Torsten]

No, you have to return a scalar value for c, i.e. c evaluated at x,z,u and DuDx (where all of these input parameters are scalars in your case).

Thus you could also write

c = (2*U_a/D_s)*(1-(x/R1)^2);   

[Shangeetha Mahendran]

thank you

[madhan ravi]

@Torsten please post it as an answer so that it would be helpful for many on how to solve pdes properly.