# How can I correctly use if and elseif?

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gblmtc el 22 de Mzo. de 2018
Comentada: Stephen23 el 22 de Mzo. de 2018
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 comentariosMostrar 1 comentario más antiguoOcultar 1 comentario más antiguo
KL el 22 de Mzo. de 2018
Editada: KL el 22 de Mzo. de 2018
Walter Roberson el 22 de Mzo. de 2018
Notice by the way that used
a=t-toe;
Also, you have not defined toe.

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Stalin Samuel el 22 de Mzo. de 2018
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 comentariosMostrar NingunoOcultar Ninguno
gblmtc el 22 de Mzo. de 2018
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 el 22 de Mzo. de 2018
Editada: Stephen23 el 22 de Mzo. de 2018
@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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### Más respuestas (1)

Stephen23 el 22 de Mzo. de 2018
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 comentariosMostrar 4 comentarios más antiguosOcultar 4 comentarios más antiguos
Stephen23 el 22 de Mzo. de 2018
Editada: Stephen23 el 22 de Mzo. de 2018
@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:
Stephen23 el 22 de Mzo. de 2018
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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