Chebyshev differential matrices code not callable

This is the code by tretfen (cheb.m):

% CHEB  compute D = differentiation matrix, x = Chebyshev grid

function [D,x] = cheb(N)
if N==0, D=0; x=1; return, end
x = cos (pi*(0:N)/N)'; 
c = [2; ones(N-1,1); 2].*(-1).^(0:N)';
X = repmat(x,1,N+1);
dX = X-X';                  
D  = (c*(1./c)')./(dX+(eye(N+1)));      % off-diagonal entries
D  = D - diag(sum(D'));                 % diagonal entries

[Walter Roberson]

What parameter are you passing? What error message are you encountering?

[Lukgaf]

Thanks, Not enough input arguments.

Error in cheb (line 4)

 if N==0, D=0; x=1;

Answer 1

[Walter Roberson]

You have to go down to the command line and call the function passing in a non-negative integer. For example,

[differ_matrix, cheb_grid] = cheb(19)

[Lukgaf]

solved thanks sir

[Walter Roberson]

I stored the code you posted in the file cheb.m and then I went to the command line and there I commanded

[differ_matrix, cheb_grid] = cheb(19)

and I got back results.

You cannot run that function just by clicking on the green Run button: you must go to the command line to run it so that you can pass in a value for N.

[Lukgaf]

Thanks