Re: Sine wave code

On Tue, Dec 29, 2020 at 12:37 PM Ian McCallion <[email protected]>
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
>
>
>
How is this?

n_points = 200;
x = linspace(-5, 5, n_points);
y_original = sin(x);
threshold = 0.5;

% Truncate the sine wave
y_truncated = y_original.*(abs(y_original)<threshold) +
threshold.*(abs(y_original)>=threshold).*sign(y_original);
y_final = y_truncated;
for k=2:n_points
if y_final(k-1)==threshold && y_final(k-1)*y_final(k)>0
y_final(k) = threshold;
end
end

clf
plot(x, y_final)

It produces the desired result for the test sine wave I put in.