Re: Sine wave code

On 29/12/2020 19:36, Ian McCallion wrote:
> On Tue, 29 Dec 2020 at 14:03, Blaz <[email protected]> wrote:
>> Hello coders
>>
>> I have a request for some sine wave code. I need to create a modified sine
>> wave where I cuttof the wave at certain value and hold this until the next
>> zero crossing (Please refer to the red marked line on the picture). The sine
>> wave (or some other for that matter) comes in as an input vector with 20
>> samples per period (this can change though from 20 to up to 40 max, but I
>> don't think this has any consequence though).
>>
>> This is part of a longer code, but I can not get this section done properly.
>> I would appreciate any kind of ideas.
> It is always difficult to get this sort of problem right using loops.
> This is not a complete solution because it does not deal with what to
> do when the signal is negative, but this can be added into the
> solution easily.
>
> So, you want the output to be
>
> - the signal from a zero-crossing until the signal reaches the reference value
> - the reference value until the signal reaches a zero-crossing
>
> Therefore the problem can be reduced to that of generating a signal to
> toggle between the two, for example:
>
> s =sin(linspace(0,2*pi,400));
> r=.8;
> toggle = [0,cumsum(max(diff(s>r),0)+min(diff(s>0),0))];
>
> # now fenerate the output signal
> out=s.*(1-toggle)+r*toggle;
>
> # and plot input and output
> plot(1:400,s,out)
>
> You will need to deal with handling the negative side of things, deal
> with zero-crossing correctly and decide whether I extended toggle to
> the correct length correctly for your problem.
>
> Cheers... Ian
>
>
This whole thing looks like a trivial piece-wise function to me. 
Detecting zero-crossing shouldn't be a problem since the function is 
based on 'sin'. so zero crossing occur when argument transition from 
0-macheps to 0+macheps and from pi-macheps to pi+macheps.

--Sergei.