Error on using ODE45 and cannot prompt output

Hi, i encounter some problem on showing the outputs for ODE45. May i know on how to solve it? I will be grateful that the solutions that provided. Thanks!

Here is the error message:

Error in p2 (line 13)

[t,C_calc]=ode45(first,timespan,C0);

Here is the codes:

clear 
close all
clc

k=1000000000;
r = 4.31*(10^-3);
kt=0.9;
D=1;
timespan=[0 30]';
C0=40000;

first=@(t,C) (C*(r-((r-kt*d)/k)*C-(kt*D)));
[t,C_calc]=ode45(first,timespan,C0);
plot(t,C_calc)
hold on

[Ilya Gurin]

Please post the full error text

[Deck Zhan Sim]

@Ilya Gurin, this is the text given

Error in p2 (line 13)

[t,C_calc]=ode45(first,timespan,C0);

[Ilya Gurin]

There's no way that can be the full text.

Answer 1

[Jan]

I get a different error message, which is very clear:

k=1e9;
r = 4.31e-3;
kt=0.9;
D=1;
timespan=[0 30]';
C0=40000;
first=@(t,C) (C*(r-((r-kt*d)/k)*C-(kt*D)));
[t,C_calc]=ode45(first,timespan,C0);

Unrecognized function or variable 'd'.

Error in solution (line 7)
first=@(t,C) (C*(r-((r-kt*d)/k)*C-(kt*D)));

Error in odearguments (line 90)
f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 106)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

plot(t,C_calc)
hold on

[Ilya Gurin]

I got that, too, but the OP seems to have a different problem.

[Jan]

As soonas I replace "d" by "D", the code runs and displays a diagram.