External function problem.

I am trying to alter this code which I have included and is functioning to use an external function.

After a few attempts but always returning errors I am at an end.

I have tried replacing line 8 and 9 with a function look up and recreating the function in the external file but it throws errors.

I believe it is a simple fix but am a bit stuck.

clear; close all; clc
balance(1) = 1000;
contribution = 1200;
M = 1; % month ticker

interest = 0.0025;
while true %this makes the program run until the break condition is met
    M = M + 1; % you need to increment months + 1 every cycle
    balance(M) = balance(M-1) + interest*balance(M-1) + contribution;
    
  if balance(end) > 500000;
      break;
  end
      
    
    
end
years = M/12; %year counter
fprintf('%g Months until $500000 reached\n', M);
fprintf('%g Years until $500000 reached\n', years);
format bank
plot(balance);
grid on
ytickformat('usd')
title('Saving 3% compound')
xlabel('Months')
ylabel('Saving balance')

Label = max(balance) %this labels the plot with max balance
txt = {'Max Balance:',Label,'\leftarrow'};
text(M,Label,txt,'HorizontalAlignment','right')

[Cris LaPierre]

What is the external function you are trying to use? What is that fuction supposed to do? Can you share it? You can attach it here using the paperclip icon. What are the error messages you are getting? Please share the entire error message (all the red text).

[Chett Manly]

The external function is to do exactly what this script does. To replace what is in the while loop with a command to use the same 'balance(M) = balance(M-1) + interest*balance(M-1) + contribution;' from an external function.

[Image Analyst]

Please attach the m-file balance.m -- which I guess is your external function.

[Chett Manly]

This is the code I am trying to make work the same as the original post but this one has to use the function externally.

clear; close all; clc
balance(1) = 1000;
contribution = 1200;
M = 1; % month ticker

interest = 0.0025;
while true %this makes the program run until the break condition is met
    M = M + 1; % you need to increment months + 1 every cycle
    account(balance, contribution, interest, M)
    
  if balance(end) > 500000;
      break;
  end
      
    
    
end
years = M/12; %year counter
fprintf('%g Months until $500000 reached\n', M);
fprintf('%g Years until $500000 reached\n', years);
format bank
plot(balance);
grid on
ytickformat('usd')
title('Saving 3% compound')
xlabel('Months')
ylabel('Saving balance')

Label = max(balance) %this labels the plot with max balance
txt = {'Max Balance:',Label,'\leftarrow'};
text(M,Label,txt,'HorizontalAlignment','right')

This is my external function file.

function  account(balance, contribution, interest, M);
    
    balance(M) = balance(M-1) + interest*balance(M-1) + contribution;

Answer 1

[Walter Roberson]

in MATLAB, assigning to one of the input parameters only causes local changes, not change to variable passed in. To change the variable you need to return the new value and assign it to the appropriate location in the calling function.

[Chett Manly]

But every time the while loops it should update the value because the line of code is asking for balance, contribution, interest, M ?

[Walter Roberson]

clear; close all; clc
balance(1) = 1000;
contribution = 1200;
M = 1; % month ticker

interest = 0.0025;
while true %this makes the program run until the break condition is met
    M = M + 1; % you need to increment months + 1 every cycle
    balance = account(balance, contribution, interest, M)
    
  if balance(end) > 500000;
      break;
  end
      
    
    
end
years = M/12; %year counter
fprintf('%g Months until $500000 reached\n', M);
fprintf('%g Years until $500000 reached\n', years);
format bank
plot(balance);
grid on
ytickformat('usd')
title('Saving 3% compound')
xlabel('Months')
ylabel('Saving balance')

Label = max(balance) %this labels the plot with max balance
txt = {'Max Balance:',Label,'\leftarrow'};
text(M,Label,txt,'HorizontalAlignment','right')

function balance = account(balance, contribution, interest, M);
    
    balance(M) = balance(M-1) + interest*balance(M-1) + contribution;

[Chett Manly]

I was so close... Sorry for the late reply, this is exactly it. Thanks!