pchip vector in ODE45 equation

Hello, I'm currently trying to make a script that takes some variable x, with some parameters p, and a fitted curve z (fitted with

FLM_Beta12 = pchip(Data(:,1),x(:,5),tSpan)

). tSpan is the first time point in the data (=ts) to the last one (=te), and looks like ts:0.01:te, Data is a column of the actual time points of measurement, and x is the measurements.

The ODE function is as follows:

 function dFTdt = Beta(t,x,p,z)
 FT=x(1);

 alpha = p(1);
 beta = p(2);
 ki=p(3);

FLM_Beta = z;
dFTdt = zeros(1,1);
dFTdt(1) = beta - FLM_Beta(t) * ki - FT * alpha;

end

For some reason when I debug the script t is always a 1x1 matrix (with the value 1). And this is how I call the ODE:

[~,yx] = ode45(@(t,x) Beta12(t,x,parameters,FLM_Beta),tSpan,FT12(1))

Where parameters is a row vector of 3 values. FT is a column vector with data. I have been trying a lot of different ways to call it, but I think the issue is with the fitted curve and that 'FLM_Beta(t)' isn't calling one value at the time. Any help, or a link in the right direction is very welcome. If I haven't provided enough details of the problem, please let me know!

Answer 1

[Torsten]

FLM_Beta12 = pchip(Data(:,1),x(:,5));
[~,yx] = ode45(@(t,x) Beta(t,x,parameters,FLM_Beta12),tSpan,FT12(1));

function dFTdt = Beta(t,x,p,z)
FT=x(1);
alpha = p(1);
beta = p(2);
ki = p(3);
FLM_Beta = z;
dFTdt = zeros(1,1);
dFTdt(1) = beta - ppval(FLM_Beta,t) * ki - FT * alpha;

end

Best wishes

Torsten.

[Philip Berg]

Thank you!!!