Help to build the logic to plot peak vs time

t = 0:0.1:10;
y = 15*sin(pi*t);

[a,b]=peakdetection(y,0.5);

if y(i) == a;

      y(i) = y(i);

else

   y(i)= 0;

end

In this i want to detect peak and valley from any type of signal. After detecting i want to plot only peak against time. All other value of y (except peak) should be zero as per my requirement.

I will appreciate if anybody help me to build this logic. I tried to use if loop but it is given error

??? Subscript indices must either be real positive integers or logicals.

Error in ==> Untitled at 7
if y(i) == a;

Regards

Jeevan Patil

Answer 1

[David]

i is an imaginary number by default causing your error.

Wrap your code in a for loop

   for ii=1:length(y)

      if y(ii)~=a
          y(ii)=0;
      end
   end

However you might find difficulties comparing floating point numbers. You may need to have some sort of compare function:

realCmp = @(x,y) abs(x-y)<1000*sqrt(eps)

And use

    if ~realCmp(y(ii),a)

However even better that that you should use

y(~realCmp(y,a))=0;

and avoid the for loop altogether

Answer 2

[Jeevan Patil]

Thanks David,

logic given by you is working. problem was not with i, it was with  logic only.

thanks again