How can I correctly use if and elseif?

Question

gblmtc 2018-3-22

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/389944-how-can-i-correctly-use-if-and-elseif

评论： Stephen23 2018-3-22

采纳的回答： Stalin Samuel

在 MATLAB Online 中打开

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?

Thank you for your help!

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 个评论
显示 1更早的评论隐藏 1更早的评论

KL 2018-3-22

编辑：KL 2018-3-22

https://www.mathworks.com/help/matlab/getting-started-with-matlab.html

and also https://www.mathworks.com/training-schedule/matlab-onramp.html

Walter Roberson 2018-3-22

在 MATLAB Online 中打开

Notice by the way that used

a=t-toe;

instead of tk = t-toe

Also, you have not defined toe.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Stalin Samuel 2018-3-22

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/389944-how-can-i-correctly-use-if-and-elseif#answer_311321

在 MATLAB Online 中打开

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 个评论
显示无隐藏无

gblmtc 2018-3-22

Thanks Samuel! I applied your function, it works but it calculates just tk=t-toe. It doesn't either add or subtract 604800. Doesn't continue and do the if . Do you know why?

Stephen23 2018-3-22

编辑：Stephen23 2018-3-22

@gblmtc: What sizes are t and toe ?

Why did you accept this answer if it does not do what you want?

请先登录，再进行评论。

Answer 2

Stephen23 2018-3-22

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/389944-how-can-i-correctly-use-if-and-elseif#answer_311338

在 MATLAB Online 中打开

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 个评论
显示 4更早的评论隐藏 4更早的评论

Stephen23 2018-3-22

编辑：Stephen23 2018-3-22

@gblmtc: I understand that there is a lot to learn, and it can seem quite daunting, but luckily MATLAB has easy-to-read documentation, which should always be the first place you look for information. You also might like to read this, it has some tips to keep in mind when learning MATLAB:

https://www.mathworks.com/matlabcentral/answers/228557-experts-of-matlab-how-did-you-learn-any-advice-for-beginner-intermediate-users