Subscripting into an empty matrix is not supported using For Loop and if Statement

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)".

I have to use the (for) Loop and if statement at my program, as all my program has been created by (if) statement and (for) Loop 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

[Tim McBrayer]

You don't really have enough information to go on here. Some clarifying questions:

1. What is the exact text of the error, and what are you doing when you receive it?
2. What size is your x array?

Some observations:

• You don't need to set k = 1; this might even interfere with type analysis
• You shouldn't use a constant for km, since it appears to be required to be length(x). Use the length expression instead.
• Your UDPN array is only being assigned 0 or 1. If this is actually the only two values that it can take, you are better off (from a HDL perspective) declaring it as boolean or fixdt(0,1,0), not double.

Answer 2

[Andrei Bobrov]

All work.

km=31416;
x = rand(km,1);
UPDN=zeros(size(x));
for k=1:km-2;
    if x(k+2)>=x(k);
        UPDN(k)=1;
    end
end
UPDN(km-1:km)=1;