Problem with function handle

The first M-file contains:

function z = FEM1D(f, N)

%%%%%%%%%%%%%%%%%%
dx=0.1;
x=[0:dx:1]';
N=length(x);

%Matrix
A=-2*diag(ones(N,1)); 
M=4*diag(ones(N,1));

%Filling matrix
for i=1:N-1
    A(i,i+1)=1;
    A(i+1,i)=1;
    M(i,i+1)=1;
    M(i+1,i)=1;
end

%%%%%%  HERE THE PROBLEM HAPPENS  %%%%%%% 
b= M*f*dx^2/6;

%boundary 
A(1,:)=0;
A(1,1)=1;
A(N,:)=0;
A(N,N)=1;

b(1)= 0; %left boundary
b(N)= 0; %right boundary

%result
z=A\b;

end

The function z = FEM1D(f, N) is called from this M-file:

tol_max = 1e-10;
N = 10;

%%%%%%%%%%%%%%%%%% example 1:
f_1 = @(x)(1-x);                          % right side
sol_1 = @(x) -1/6*x.*(2 - 3*x + x.^2);    % excat result

%%%%%%%%%%%%%%%%%% example 2:
a=0.5;
c=100;
f_2 = @(x) c*(2*(2*a^2*c - 4*a*c*x + 2*c.*x.^2 - 1).*exp(-a^2*c + 2*a*c*x - c*x.^2));
sol_2 = @(x) (exp(-(x-a).^2*c) - exp(-(a).^2*c));

%%%%%%%%%%%%%%%%%% solve example 1:
z_1 = FEM1D(f_1 , N);
x = linspace(0,1,N+1);
sol_dis_1 = sol_1(x)';
err = max(z_1 - sol_dis_1);
if(abs(err) > tol_max)
    error('error example 1')
    z_1 - sol_dis_1
end

%%%%%%%%%%%%%%%%%% solve example 2:
z_2 = FEM1D(f_2 , N);
x = linspace(0,1,N+1);
sol_dis_2 = sol_2(x)';
err = max(z_2 - sol_dis_2);
if(abs(err) > tol_max)
    error('error example 2')
    z_2 - sol_dis_2
end


disp('code is okey')

What do I have to change in the first file to make the second file work? The line in the first file where the error happens I' ve marked with

%%%%%%  HERE THE PROBLEM HAPPENS  %%%%%%%

Answer 1

[James Tursa]

f by itself is just a function handle, not the function handle evaluated for any input. You need to give f an input. E.g.,

b= M * f(x) * dx^2 / 6;

Answer 2

[Vinayak Mohite]

Hi Salih,

The problem in your code is one cannot multiply the function handle with a scalar. Consider passing a parameter to the function handle.

e.g. change

b= M*f*dx^2/6;

to

b= M*f(-11)*dx^2/6;

You can use any value instead of -11.