# Error when using the function ODE45

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Stephanie Velasco on 24 Feb 2017
Edited: Walter Roberson on 25 Feb 2017
I have written to the following function to solve a differential equation using ODE 45, but i always seem to come across an error saying the "Inputs must be floats, namely single or double.". I am trying to solve for dt/dx,t(x)= 1/(a*x^(0.6)-b*x)), to find the time. but i get an error every time. since I have x in the equation idk what I'm doing wrong.
script
x_interval=[0.5 10];
t0 = ;
[x,t] = Ode45(diff_,x_interval,t0);
function dt/dx = diff_(x,t)
a = 10;
b=0.5;
syms x;
t = (1/(a*x^(0.6)-b*x));
dt_dx =t;
end

John D'Errico on 24 Feb 2017
How is this question significantly different from the last time you asked it, asking for help on solving the same question? Please stop making multiple postings for the very same problem.
Stephanie Velasco on 25 Feb 2017
I wasn't sure if this one was clear enough, Im sorry about that. Have a blessed day

John Chilleri on 25 Feb 2017
Hello,
You just need to change a few things:
Script - missing an @ symbol.
x_interval=[0.5 10];
t0 = 0;
[x,t] = ode45(@diff_,x_interval,t0);
Function - don't use sym and you have a / in the name.
function dt_dx = diff_(x,t)
dt_dx = (1/(10*x^(0.6)-.5*x));
end
I simplified your function, but you can leave it as,
function dt_dx = diff_(x,t)
a = 10;
b=0.5;
t = (1/(a*x^(0.6)-b*x));
dt_dx =t;
end
Hope this helps!

#### 1 Comment

Stephanie Velasco on 25 Feb 2017
Thank you so much! Have a great day!