need difference equation and for loop help

[ethers0n]

I'm attempting to solve a difference equation

y(k+1) = -0.5*y(k) + x(k)

where y(0) = 0 and x(k) is in my case a unit step function ie = 1

well, i'm trying to solve this using a for loop, but am having some trouble. The code i've generated gets an error, "Index into matrix is negative or zero."

Any ideas?
My code is below.

k = 0 ; %counter variable
y = 0; %y(k)
x = 1; %x(k), unit step function

for k = 0 : 5

y(k+1) = -.5*y(k) + x;

y(k) = y(k+1)

end

 

[GregLocock]

Well, the error message seems pretty informative.

If k is zero and you call y(k) what else would you expect?



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[xnuke]

MATLAB matrix indices start at 1, not 0.

xnuke
"Do you think you used enough dynamite there, Butch?"
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