Help with assignment on functions

I cannot understand how to complete this at all:

1. The cost of sending a package by an express delivery service is $15 for the first two pounds, and $4.25 for each pound over two pounds. Write a program that computes the cost of mailing the packages. Your program must use a function to calculate the cost. Use the test data: 1.5 16 103 lbs The data should be read by the main program from a text file. The data is passed to the function. The results and any other output should be printed by the main program.

 Function I have so far:

    function x=cost(a)
    for k=1:length(a)
    if a(k)<= 2
        x=15;
    else a(k)>2
        x=15+4.25*(a-2); 
    end
  end

Program

clc
clear
disp(' name')
disp(' Project 8 problem 1')
ffrd1=fopen('weight.txt','rt');
a=fscanf(ffrd1,'%f',3);
fclose(ffrd1);
co=cost(a)
fprintf('%5f',co)

This is the error I'm getting:

Error in cost (line 2) for k=1:length(a)

Output argument "x" (and maybe others) not assigned during call to "/Users/jdickman/Desktop/Matlab/cost.m>cost".

Error in a10_1 (line 8) co=cost(a)

Answer 1

[Azzi Abdelmalek]

function x=cost(a)

This mean you are calculating x depending on the value of a. In your code x is not calculated. You should correct this (elseif instead of else)

 if a(k)<= 2
        x=15;
 elseif a(k)>2
        x=15+4.25*(a-2); 
 end

%or

if a(k)<= 2
      x=15;
else
      x=15+4.25*(a-2); 
end

Answer 2

[Josh Dickman]

Oh okay. So that helps, but now the problem is the function is not calculating the first weight (1.5) correctly. It should read be calculated as 15 (since it is less than 2lbs), but instead the function is putting it through the x=15+4.25*(a-2) part.

function x=cost(a)
for k=1:length(a)
if a(k)<= 2
        x=15;
elseif a(k)>2
        x=15+4.25*(a-2); 
end
end

Which outputs:

12.875000

74.500000

444.250000

the 12.875 is the 1.5lb weight, but it should be 15

[Torsten]

function x=cost(a)

for k=1:length(a)

if a(k)<= 2

        x(k)=15;

elseif a(k)>2

        x(k)=15+4.25*(a(k)-2);

end

end

Best wishes

Torsten.

Answer 3

[Josh Dickman]

Awesome! Thanks for the help. Could you explain why that worked?

[Torsten]

Sure.

In your version, the x variable looks like

for k=1: x=15

for k=2: x=[12.875000 74.500000 444.250000]

for k=3: x=[12.875000 74.500000 444.250000]

In my version, it looks like

for k=1: x=15

for k=2: x=[15 74.500000]

for k=3: x=[15 74.500000 444.250000]

So don't set the return vector x as a whole for each k, but elementwise.

And you should allocate the x vector as

x=zeros(length(a))

when you enter your cost function.

Best wishes

Torsten.

[Josh Dickman]

Ok, thanks! That was really helpful!

Answer 4

[Andrei Bobrov]

function c = cost(a)
    n = numel(a);
    c = 15*ones(n,1);
    k = a(:) - 2;
    l0 = k > 0;
    c(l0) = c(l0) + k(l0)*4.25;
end

Answer 5

[Mainak Kundu]

function [cost]=package_weight(w)

if w<=2

cost=15;

else cost=15+4.25*(w-2)

end