Unrecognized function or variable 'Newton_Starbucks'.

T0 = 140; %intial temperature of the body
T20 = 80; %temperature of the body after 20 minutes
TR = 22; %temperature of the air
tspan = [0 35]

tspan = 1×2

0 35

[t,T] = ode45(@Newton_Starbucks,tspan,T0)

Unrecognized function or variable 'Newton_Starbucks'.

Error in odearguments (line 92)
f0 = ode(t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 107)
odearguments(odeIsFuncHandle,odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);

Answer 1

[the cyclist]

I searched the internet for "Newton_Starbucks". The only link I found was this one. If that's relevant, then it seems to me that you need to define

function Tprime=Newton_Starbucks(t,T)
    r=.001;
    T_ambient=75;
    Tprime=-r*(T-T_ambient);
end

and make sure your code can find it.

Next time you post a question, I suggest you read this guide about how to ask a good question.