Subscripting into an empty matrix is not supported

Hi There,

I have the following simple Matlab code, and I'm trying to implement the HDL code for it. but I got this error "Subscripting into an empty matrix is not supported" for "x(k+2)".

is there anyone could help me on that?

x=amp*sin(2*f*t);

k=1;

km=31416;

UPDN=zeros(1,km,'double');

for k=1:1:km-2;

    if x(k+2)>=x(k);

        UPDN(k)=1;

   else 

        UPDN(k)=0;

   end

end

for k=km-1:1:km;

    UPDN(k)=1;

end

Answer 1

[Andrei Bobrov]

x = x(:);
UPDN = [x(2:end);[1;1]] >= [x(1:end-2);[0;0]];

[Tamer]

This answer is not working with me, it solved the problem, but I still want the If function and for statement at my program.

Do you have another suggestion please?

Answer 2

[Tamer]

Thank you Andrei,

your solution fixed my problem but my Matlab program has lots of (for & if statement). Do you have another solution for this problem ? I have to keep the if & For statement as showing at the example below.

for p=2:pp-2

    if (dero(p)+1 == dero(p+1)&& dero(p)+2 == dero(p+2));

       dero2(p+1)=0;

    end

end

Thanks, -- Tamer

[Andrei Bobrov]

dero2 = dero;
dero2(conv2(diff(dero(:)),[1;1])==2) = 0;

or

dero2(strfind(diff(dero(:)),[1 1])+1) = 0;

[Tamer]

Andrei,

I have to keep the (if)statement and (for) loop at my program, because I have lots of (for) loops and (if) statement at my program. do you have another solution by keeping (if) and (for)?

Thanks for you help -- Tamer

[Tamer]

Andrei,

This solution is not working at Matlab 2013a, do you have any other solution?

Thanks,

Tamer