External function problem.

Question

Chett Manly 2021-9-18

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1455859-external-function-problem

评论： Chett Manly 2021-9-21

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

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')

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Image Analyst 2021-9-18

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

Chett Manly 2021-9-18

在 MATLAB Online 中打开

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;

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Answer 1

Walter Roberson 2021-9-18

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1455859-external-function-problem#answer_790384

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.

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Walter Roberson 2021-9-19

在 MATLAB Online 中打开

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;