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Please help! "Error: Function definitions are not permitted in this context. "

Asked by Agata on 16 Oct 2011
Latest activity Edited by Gedion Teklewolde on 26 Mar 2014 at 2:48

Hello! I'm extremely new to Matlab, and I'm working on a homework problem, and I keep coming up with an error... I've written my functions, and defined some variables to be plugged into them. I can't even call my functions, because I get the error for writing them.

This all has to be in one m-file so I cannot save the functions in different ones... I'm not sure what to do :(

function [x,y,vx,vy] = trajectory(t,v0,th0,h0,g)      
x = v0 .* cos(th0) .* t;
y = h0 + (v0 .* sin(th0) .* t) - ((1./2) .* g .* (t.^2));
vx = v0 .* cos(th0);
vy = (v0 .* sin(th0)) - (g .* t);
function y = height(t,v0,th0,h0,g)
[x,y,vx,vy] = trajectory(t,v0,th0,h0,g);  
%(b)
v0 = 20;
th0 = 45;
h0 = 5;
g = 9.81;
t = linspace(1,4,400);
y = height(t,v0,th0,h0,g)

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Agata

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4 Answers

Answer by Fangjun Jiang on 16 Oct 2011

You need to understand the difference between M-script and M-function.

If the first line of your .m file is a function definition like you have in the code. This .m file is a M-function.

If the first line of your .m file is not a function definition, but other M command or M code, the .m file is called M-script.

You can not have M-function definition in M-script. That is the error message tries to tell you.

You can save the two functions you have in two .m file and then write a script to call the function.

See Functions and Scripts

Please vote here to voice your request. http://www.mathworks.com/matlabcentral/answers/7690-please-vote-if-you-want-to-have-m-function-in-m-script

2 Comments

Jan Simon on 16 Oct 2011

It becomes an evergreen and should be included in the FAQ.

binh on 12 Apr 2013

thanks for your answer! I split this function to another .m file and it worked!

Fangjun Jiang
Answer by Walter Roberson on 16 Oct 2011

In addition to what Fangjun wrote:

When you are not already executing within a given file, MATLAB can only find the very first function in that file, and that first function name must be the same name as the file.

Therefore, the order of functions in the file should be that the very first one is the "driver" function (the one that sets up everything and calls the other functions to do the work), and the functions that do the internal work should be after that in the file.

If you look at the function order you have coded above, you have coded the internal routine first, and then coded a routine that calls that internal routine. You would, however, not be able to activate that second routine from the MATLAB command line.

So... what you need to do is take the line that start at %(b) through to the end of the file, and move those lines to the beginning of the file, and then you have to insert a "function" line at the very top, naming it appropriately for your assignment conditions. I can see from the code that those lines set things up and then call the internal routines, so those lines should be in the first function.

0 Comments

Walter Roberson
Answer by Kamil Kasic on 28 Jan 2014
Edited by Walter Roberson on 28 Jan 2014

What is wrong here?

basic example from Matlab help:

function y = average(x)
if ~isvector(x)
    error('Input must be a vector')
end
y = sum(x)/length(x); 
end
  function y = average(x)
  |
Error: Function definitions are not permitted in this context.

1 Comment

Walter Roberson on 28 Jan 2014

You need to store that in a file named average.m and run it from the file. You cannot create functions at the command prompt.

Kamil Kasic
Answer by Gedion Teklewolde on 26 Mar 2014 at 2:47
Edited by Gedion Teklewolde on 26 Mar 2014 at 2:48

Even when it is saved in appropriate name file.m it still fails.

clc
clear
clc
%
% Newton-Raphson method
%
function [x0,err] = newraph(x0)
maxit = 100;
tol = 1.0e-6;
err = 100.0;
icount = 0;
xold =x0;
while (err > tol & icount <= maxit)
icount = icount + 1;
f = funkeval(xold);
df = dfunkeval(xold);
xnew = xold - f/df;
if (icount > 1)
err = abs((xnew - xold)/xnew);
end
fprintf(1,'icount = %i xold = %e f = %e df = %e xnew = %e err = %e \n',icount, xold, f, df, xnew, err);
xold = xnew;
end
%
x0 = xnew;
if (icount >= maxit)
% you ran out of iterations
fprintf(1,'Sorry. You did not converge in %i iterations.\n',maxit);
fprintf(1,'The final value of x was %e \n', x0);
end
function f = funkeval(x)
f = x + log(x);
function df = dfunkeval(x)
df = 1 + 1/x;

0 Comments

Gedion Teklewolde

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