Need help: Script working in 2012b but not 2013b???

Been working my way through a matlab tutorial. The scripts in the tutorial all have a similar layout:

if true
function solve_bernoulli 
% Function to solve dy/dt = (t*y^4+2y)/6 
% from t=tstart to t=tstop, with y(0) = initial_y 
% Define parameter values below. 
tstart = 0; 
tstop = 20; 
initial_y = -2; 

 [t_values,sol_values] = ode45(@diff_eq,[tstart,tstop],initial_y); 

 plot(t_values,sol_values); 

 function dydt = diff_eq(t,y) % Function defining the ODE 
 dydt = (t*y^4+2*y)/6; 
 end 

 end
end

The layout is as below:

• function function_name
• %stuff in the function
• %May even include an actual embeded function (as the example above has)
• end

Every time I run it I get the error:

"The selected section cannot be evaluated because it contains an invalid statement"

and in the command window:

" function solve_bernoulli | Error: Function definitions are not permitted in this context."

HOWEVER , this script works in the tutorial writings computer using 2012b. So how can this not work on my 2013b version???

Need help as this is driving me nuts!

Answer 1

[mark]

Okay, I found out why, and it revolves around me being a lazy tw@;

I don't normally " save " scripts — instead I choose to use " Run and Advance " as it generally runs scripts fine, allowing you to test them out before you save it. It seems that, although I was saving the function first, using " Run and Advance " on a function doesn't work (at least a function in the form above). You actually need to use the more general, and obvious, " Run ".

I feel like an idiot but I'm glad I found it out instead of giving up on it.

Answer 2

[Daniel Shub]

The above code will not work in ANY version of MATLAB because

if true
function solve_bernoulli 
...

is not valid. The FUNCTION keyword can only be used in an m file. Further, the first line of code in the m file must begin with the FUNCTION keyword. Despite your claims, removing

function solve_bernoulli

and the corresponding end will not solve the problem since it will leave

function dydt = diff_eq(t,y)

in the middle of the m file, which again is not valid (or you are leaving out part of the code).

[mark]

I'm sorry but it works.

if true

    function solve_bernoulli 
% Function to solve dy/dt = (t*y^4+2y)/6 
% from t=tstart to t=tstop, with y(0) = initial_y 
% Define parameter values below. 
tstart = 0; 
tstop = 20; 
initial_y = -2; 
 [t_values,sol_values] = ode45(@diff_eq,[tstart,tstop],initial_y); 
 plot(t_values,sol_values); 
 function dydt = diff_eq(t,y) % Function defining the ODE 
 dydt = (t*y^4+2*y)/6; 
 end 
 end

end

Copy and paste that into a script. Save it. Then click the green play button.

My issue was that I wasn't playing the script properly. I don't quite know why the guy writes scripts in this way, but he does.

[Daniel Shub]

No it doesn't ...

>> temp
Error: File: temp.m Line: 3 Column: 5
Function definitions are not permitted in this context.

MATLAB has never permitted code like this.

Answer 3

[mark]

*writers computer

I should probably add that I can get the script to work if I remove the "function function_name" part and reorganise the script. But, I don't understand how it doesn't work on my computer.