I can't run that code (i'm new)

Hello,

I am very new to Matlab and I can't run that code with the following error: Error: The input character is not valid in MATLAB statements or expressions.

Here is the code (I didn't write it):

function err=bdf2(x0=1,h=0.1)

% formule de differences finies BDF2

    diff = (3*f(x0)-4*f(x0-h)+f(x0-2*h))/(2*h);

err = abs(diff-df(x0));

fprintf(' x0 %e h %e erreur %e \n',x0,h,err)

% function f

function funct=f(x)

    funct = sin(x);

% derivative f

function dfunct=df(x)

    dfunct = cos(x);

[Guillaume]

We need the full text of the error message, particularly the bit that tells you which line is causing the error.

I've formatted your code as code, but please get rid of the useless blank lines you put in there and next time use the {}Code format button.

[Guillaume Fleurisson]

Thanks for you answer ! This is the full error message (_672bf7cd7e95dc88638c440f3215c7e2_bdf2 is the name of the file)

>> _672bf7cd7e95dc88638c440f3215c7e2_bdf2
 _672bf7cd7e95dc88638c440f3215c7e2_bdf2
 ↑
Error: The input character is not valid in MATLAB statements or expressions.

And sorry for the blank lines, I didn't see the Code format button :/

Answer 1

[Steven Lord]

function err=bdf2(x0=1,h=0.1)

That's not valid MATLAB syntax. If you want h to default to 0.1 and x0 to default to 1 you can do something like:

function err=bdf2(x0, h)
if nargin < 2
  h = 0.1;
end
if nargin < 1
  x0 = 1;
end

Answer 2

[Geoff Hayes]

Guillaume - since your file has a function named bdf2 then your m-file must be named the same way as bdf2.m. You would then call it from the command line as

 bdf2(42,43)

where you would pass in two value for x0 and h. (The 42 and 43 I'm passing in are just for illustration.)

I am surprised by the function signature though

 function err=bdf2(x0=1,h=0.1)

I didn't realize that you could provide default values for your input parameters. Are you sure that this is valid?

Answer 3

[Guillaume Fleurisson]

This is working, thank you all very much for your fast answers ! :)