Is there an efficient way to write a piecewise function ?

Question

sun 2021-8-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1440054-is-there-an-efficient-way-to-write-a-piecewise-function

评论： Star Strider 2021-8-25

采纳的回答： Star Strider

在 MATLAB Online 中打开

Hi,

I have a very long 1 x 4000 temperature vector, A = [a1 a2 a3 a4 a5 a6 a7 .... a4000].

I also have the hours vector T = [t1 t2 t3 t4 t5 .....t4000]. A and T are given.

Now, I wish to have a stair function, such that,

if  0<=t<t1 func = a1; 
if t1<=t<t2 func = a2;
if t2<=t<t3 func = a3;...

In the stuff I am doing, I used to use "piecewise" function for small number of A and T for testing (maybe just a1 to a10). So, I can manually wrote pieces one by one. Now, I need to use the real stuff A,which is very long. I cant do this one by one anymore. So, my question is, is there a way I could make a piecewise stair function for given A and T.

Please do notice that:

This stair function will be feed into integration later. It must be ONE function, that's why I was using "piecewise" (It works well). In other words, I do NOT use it just for plot.
Honestly, I dont know this piecewise function will allow me to manually write that many pieces to a4000 or not.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Star Strider 2021-8-24

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1440054-is-there-an-efficient-way-to-write-a-piecewise-function#answer_773764

在 MATLAB Online 中打开

The condition statements wr.t. ‘t’ need to be revised slightly, and with that change, this works:

t1 = 5;

t2 = 7;

t3 = 15;

a1 = @(t) sin(t);

a2 = @(t) 5;

a3 = @(t) cos(t);

func = @(t) a1(t).*(0<=t & t<t1) + a2(t).*(t1<=t & t<t2) + a3(t).*(t2<=t & t<t3);

tv = linspace(-5,20);

figure

plot(tv, func(tv))

grid

Note — While all the ‘a’ values are functions of ‘t’ for simplicity, they can be constants.

.

2 个评论
显示无隐藏无

sun 2021-8-25

thank you

Star Strider 2021-8-25

As always, my pleasure!

.

请先登录，再进行评论。

Answer 2

Bruno Luong 2021-8-24

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1440054-is-there-an-efficient-way-to-write-a-piecewise-function#answer_773779

在 MATLAB Online 中打开

tempfun = @(x) interp1([0 T], A([1:end end]), x, 'previous');
temp = tempfun(whatever_query_t); 

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

sun 2021-8-25

thank you

请先登录，再进行评论。