MATLAB: Temperature Dependent parameters in PDE toolbox

Question

Hello !

I'm trying to implement a Phase Change Material in PDE Toolbox in a 2D model, so that I build a model and I need to use Temp-dependent heat capacity and conductivity. I define the capacity as follow and it works well

d = @(region,state) 900.*(4250 +(15000-4250).*exp(-((21.7-state.u)./3).^2)); %Cp*rho
...
specifyCoefficients(modele,'m',0,'d',d,...,'face',1);

But to define conductivity I need a stattement condition on temperature. So I wrote a function in c.m

function y = c(region,state)
if state.u < 21.7
    y = 0.25;
else
    y = 0.20;
end

And I call the function in the main program as follow ..

cond = @c
specifyCoefficients(modele,'m',0,'d',d,'c',cond,...,'face',1);

But when I run the program , I get the following error:

Error using formGlobalKF2D
Coefficient evaluation function, "c", was requested to calculate coefficients at 276 locations so should have returned a
matrix with 276 columns. Instead it returned a matrix with 1 columns.

Does someone know how to implement a statement condition on my coefficients ?

Answer 1

I found by myself what was my mistake ! The c coefficient has to be a matrix of N lines ( number of equation) and Nr columns ( length(region.x) ) !

So it is sufficient to do modify the code as follow :

function y = c(region,state)
Nr = length(region.x)
y = zeros(1,Nr)
if state.u < 21.7
  y(1,:) = 0.25;
else
  y(1,:) = 0.20;
end