# How can I correctly use if and elseif?

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gblmtc 2018 年 3 月 22 日
コメント済み: Stephen23 2018 年 3 月 22 日
Hi there! I'm a newbie on the Matlab and I just don't know how to write this function.
I have two inputs : t and toe
I have to calculate
tk = t-toe
if tk > 302400 tf = tk - 604800
if tk < -302400 tf tk + 604800
I created this function :
function [tk] = time(a)
a=t-toe;
if tk>302400; tf = tk-604800;
elseif tk<-302400; tf = tk+604800;
end
end
when I run this function I get this error.
% Undefined function 'time' for input arguments of type 'double'.
what does it mean "input arguments of type double"? what is the double there?
P.S: How can I learn more quickly this program? It seems a bit complicated for me considering I've never learnt programming before. Could I find some exercises to help me learn it?
##### 3 件のコメント表示非表示 2 件の古いコメント
Walter Roberson 2018 年 3 月 22 日
Notice by the way that used
a=t-toe;
Also, you have not defined toe.

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### 採用された回答

Stalin Samuel 2018 年 3 月 22 日
create a file with below code
function [tf] = time(t,toe)
tk=t-toe;
if tk>302400; tf = tk-604800;
elseif tk<-302400; tf = tk+604800;
end
end
while saving the code you must use "time" as file name.
##### 2 件のコメント表示非表示 1 件の古いコメント
Stephen23 2018 年 3 月 22 日

@gblmtc: What sizes are t and toe ?
Why did you accept this answer if it does not do what you want?

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### その他の回答 (1 件)

Stephen23 2018 年 3 月 22 日
I guess that some of the inputs are non-scalar, in which case you should use indexing:
function tk = time(t,toe)
tk = t-toe;
idx = tk>302400;
tk(idx) = tk(idx)-604800;
idx = tk<-302400;
tk(idx) = tk(idx)+604800;
end
##### 6 件のコメント表示非表示 5 件の古いコメント
Stephen23 2018 年 3 月 22 日
Yes, you are right! Sometimes it is really really daunting. Sometimes I just say it is not for me and I just can't do it. Thanks for your help!

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