Error using feval and Invalid function name

Please friends, i will aprecciate your help,

I have this code:

function I= Trapecios(f,a,b,n)
%Fórmula Trapecios compuesta
h=(b-a)/n;
x=a:h:b;
x=x(:);
for i=1:n-1
    k1=feval(f,x(i));
    pesos=[1 2*ones(1,n-1) 1];
    I=h./2*sum(pesos*k1);
end

end

So when I input the arguments, issues these messagges:

>> Trapecios('x/56',-56/2,9*56/10,8)

Error using feval

Invalid function name 'x/56'.

Error in Trapecios (line 7)

k1=feval(f,x(i));

Answer 1

[Voss]

You can use an anonymous function, e.g., f = @(x)x/56, or a named function, rather than a character array (f = 'x/56') for feval.

Trapecios(@(x)x/56,-56/2,9*56/10,8) % using anonymous function @(x)x/56

ans = 43.1200

Trapecios(@divide_by_56,-56/2,9*56/10,8) % using a handle to a named function, defined below

ans = 43.1200

Trapecios('divide_by_56',-56/2,9*56/10,8) % using the name of the function

ans = 43.1200

function out = divide_by_56(x)
out = x/56;
end


function I= Trapecios(f,a,b,n)
%Fórmula Trapecios compuesta
h=(b-a)/n;
x=a:h:b;
x=x(:);
for i=1:n-1
    k1=feval(f,x(i));
    pesos=[1 2*ones(1,n-1) 1];
    I=h./2*sum(pesos*k1);
end
end

[Víctor Sánchez]

It worked bro!!!!... Thank you thank you a lot. !!!

[Voss]

No problem!