I tried to call a function but it failed

When i tried to return a value from the function (rate) to main file it failed and it shows undefined variable R_tow.

%main file

clc
clear all
close all
T=1;
tow_min=0;
tow_max=T;
tow=0.5
while (tow_max-tow_min)>0.02
    tow_bar=(tow_max+tow_min)/2;
    if crn(tow_bar)==crn(tow_min)
        tow_min=tow_bar;
    else
        tow_max=tow_bar;
    end
end
tow0=tow_bar;
disp("tow0="+tow0);
rate(tow0);
("R_tow="+R_tow);
plot(R_tow,tow0);

 function R_tow=rate(tow)

PH0=0.1
Pa=10;
Q=20;
y=0.1;
N=3;
yi=[1,3,5];
Pdbar=0.2;
Pi=[3,4,2];
alpha=sqrt((2*y)+1)*qfuncinv(Pdbar);
beta=0
    for i =2:N
    x=1+((Pi(i)*yi(i))/((1+sum(Pi(i)*yi(3:N)))));
    beta=beta+log2(x);
    end
fs=100000;
z=1+sum(Pi(2:N).*yi(2:N));
S=(Pa*yi(1))/z;
x1=(1-(qfunc(alpha+(sqrt(tow*fs)*y))))
y1=log2(1+(((tow*Pa/1-tow)-sum(Pi(2:N)))*yi(1))/z)
R_tow=PH0*(1-tow)*x1*y1+beta;
%disp(R_tow)
 end
 
 

[Navid Zolfaghari Moheb]

So change the last four line of your code to:

disp("tow0="+tow0);

R_tow = rate(tow0);

("R_tow="+R_tow);

plot(R_tow,tow0);

you have a function that returns a value and you call that value "R_tow". But this is local only to that function. Now if you want to use it in another function you have to tell that function to get the output from my 'rate' function and call it "R_tow". Having it defined as "R_tow = rate(tow)" in function does not mean that whenever I run rate(tow), I will have an output called R_tow. It means that it has an output but you have ot name it. For example, in your first function, you could have "y=rate(tow)" or "zeta = rate(tow)" or in this case "R_tow=rate(tow)".

[Barry Allen]

Thanks

It helped

Answer 1

[Walter Roberson]

It is fundamental to the idea of functions in all programming languages that the variable names inside the function are internal to the function, that assigning to a variable inside the function does not affect the calling environment unless special arrangements are made.

Your assigning to the R_tow variable that belongs to the function rate() does not affect any variable outside of rate().

In order to get what you want, at the place you have

rate(tow0);

You need instead

R_tow = rate(tow0);

This R_tow is not the same variable as the one inside of rate(). Assignment of results is positional not according to name.