Function can't see variable

Question 1

Write a function-file can be used to calculate

equivalent resistance of n parallel connected resistor

function Req = equiv_parallel(r)
%r is an input of length n
%req is an output
%usage req= equiv_parallel(r)
%resistances' values
% for example r=[1 2 3 4 5]
r = [1 2 3 4 5]; %resistances' values
n = length(r); %number of resistor
Req = 1/sum(1./r); %sum of all parallel resistor
end

when I'm trying to run this code write as equiv_parallel(r) , matlab gives me "Undefined function or variable 'r'."

Answer 1

[Image Analyst]

You're probably just clicking the green run triangle without passing in anything for r. Try assigning r first and then calling the function. And DON'T clobber the passed-in r by reassigning it to that vector [1,2,3,4,5]!

%r is an input of length n
%req is an output
%usage req= equiv_parallel(r)
%resistances' values
% for example r=[1 2 3 4 5]
r = [1 2 3 4 5]; %resistances' values
% Now call the function
Req = equiv_parallel(r)

Req = 0.4380

function Req = equiv_parallel(r)
n = length(r); %number of resistor
Req = 1./sum(1./r); %sum of all parallel resistor
end

[Ahmet Can Seker]

thank you for your answer

%question 1

%write a function-file can be used to calculate

%equivalent resistance of n parallel connected resistor

function Req = resistors(r1,r2,r3,r4)

%r is an input of length n

%req is an output

r = [r1, r2, r3, r4];

Req = 1/sum(1./r); %sum of all parallel resistor

end

I wrote as resistors(1, 2, 3, 4) and it accept