Using previous value to get the next in for loop

Hi guys,

I have what I believe is a simple problem but I cannot manage to get to work!

I have a (6003 x 1) vector of u-values. I want to create a vector of y-values which are defined using the previous value and its corresponding u-value as such:

h=0.1;

y(1) = 0

y(2) = y(1) + h.*u(1)

y(3) = y(2) + h.*u(2) ... etc.

At the moment, my loop is defined as such:

h=0.1;

y(1) = 0;

for k=2:6003

y(k) = y(k-1) + h.*u(k-1)

end

But this makes my command window seemingly run forever. How do I correct this code? Any help is much appreciated!

Answer 1

[Stephan]

The semicolon operator supresses outputs to the command window:

h=0.1;
y(1) = 0;
for k=2:6003
    y(k) = y(k-1) + h.*u(k-1); 
end

[Stephen23]

"But the much better news for you is that you dont need a for loop"

True, but you do realize that your "don't need a loop" code uses data from the loop?

Did you check the output values?

[Stephan]

oops ;-) - corrected - thank you @Stephen Cobeldick

[Joel Childs]

Thank you both of you!

Answer 2

[Stephen23]

"But this makes my command window seemingly run forever."

So far no one has actually addressed why your code is inefficient, in particular:

1. lack of array preallocation before the loop,
2. pointless printing to the command window.

Your code will be quite efficient once you deal with both of those, for example:

h = 0.1;
n = 6003;
y = zeros(1,n);
for k = 2:n
    y(k) = y(k-1) + h.*u(k-1);
end

[Joel Childs]

Much obliged, thank you