# Matlab help

• MATLAB

## Main Question or Discussion Point

I want to find q501 for the difference equation:

qn=qn-1 - 0.001 q2n-2
n≥2,
q0=1,
q1=2

I thought it's easier to do this on Matlab & I tried to write a script file for this problem:

Code:
k=0.001
q(1)=1
q(2)=2
for n=1:502
q_n=q_n-1-k*(q_n-2)^2
end
I don't know why my code isn't working/giving the right answer. Does anyone know what's the problem with this script?

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f95toli
Gold Member
You are not indexing the array in the right way
Element n of a vector q is written q(n) in Matlab (with the first element having index 1, not zero as in some other programming languages).

Try
Code:
k=0.001
q(1)=1
q(2)=2
for n=3:502
q(n)=q(n-1)-1-k*q(n-2)^2
end