Matlab Function block code

23 次查看（过去 30 天）
John Whelan
John Whelan 2017-5-24
评论： Les Beckham 2017-6-5
Hi, I am new to Matlab. I have a merge block that outputs either a 1 or 0. What I want to do is; If the input to the function block is 0, i want the output to be 0 and not be able to change back to 1. if the input is 1 i want the output to be a 1 but be able to change to a 0. is it possible to implement this? thank you in advance!

请先登录，再回答此问题。

采纳的回答

Honglei Chen
Honglei Chen 2017-5-24
I think you can use persistent variable to set a flag in the function block. If the input is ever 0, then you just ignore the future input. Something like this
function y = fcn(u)
persistent flag
if isempty(flag)
flag = true;
end
if flag
y = u;
if u == 0
flag = false;
end
else
y = 0;
end
end
HTH
  4 个评论
显示 2更早的评论
Honglei Chen
Honglei Chen 2017-5-24
编辑：Honglei Chen 2017-5-24
You can try to use a switch block at the input, as shown here
https://www.mathworks.com/help/simulink/slref/switch.html
so that one of the input is to your real input and the other one to a constant 1. For the condition, you can use a clock
https://www.mathworks.com/help/simulink/slref/clock.html
and compare its output with the 0.5 threshold.
HTH
Walter Roberson
Walter Roberson 2017-5-24
编辑：Walter Roberson 2017-5-24
Add a Clock or Digital Clock block and run the input to the second port. Then,
function y = fcn(u, t)
persistent lastval
if isempty(lasval); lastval = cast(1, class(u)); end
if t <= 0.5
y = u;
else
y = cast(u & lastval, class(u));
lastval = y;
end

请先登录，再进行评论。

更多回答（1 个）

Les Beckham
Les Beckham 2017-5-25
Note that you can also do this with simple Simulink blocks (and no Matlab function block). If you don't have to protect against the input being zero during the first 0.5 seconds, it only takes two blocks. With the protection, it takes five. Here is an example. Be sure that you set the initial condition on the Memory block. You probably also want to make sure the decimation on the Clock block is set to 1.
<<
>>
  6 个评论
显示 4更早的评论
Walter Roberson
Walter Roberson 2017-6-5
编辑：Walter Roberson 2017-6-5
I think you are right that
y = cast(u & lastval, class(u));
could be abbreviated as
y = u & lastval;
unless somehow the block was being called multiple times with different signal types (or unless somehow the signal type of the input can change during execution -- just because I can't think of a way that could happen doesn't mean it isn't possible.)
But mostly I think I put in the explicit typecast to be sure that code generation would know for sure what the output type would be, instead of code generation having to deduce that it is holding the correct type because of a persistent variable assigned to in the past.
Les Beckham
Les Beckham 2017-6-5
I agree completely that this is good 'defensive programming' practice.
I do like to encourage the use of built-in Simulink blocks where possible as I've found them more efficient and portable (across versions, etc.).
Of course, the original question was about a Matlab function block implementation. I just wanted to show that there was an alternative.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 General Applications 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by