how to call a string into a function

I am currently working on a GUI wherein you can input numbers then it will graph the answer. The function is a differential equation and im using ode45. How am i going to use the inputted number to the function?

For example:

function dxdt=rhs(t,x);

     dxdt= 3*exp(-t);
 end

I need the 3 there to be a user inputted number.

I will really appreciate it. Thank you so much :)

Answer 1

[madhan ravi]

help str2func
help input

[Ma.Cathyrine Ravina]

where should i put the str2func?