How to divide a part of array to the another part of it?

For example, i had a array has 28 numbers(non integer), and since these values depending on other variable and changing, i want to find first 1/5 part of it divided to last 1/5. The sum of the first 5 terms over sum of the last 5 terms.

Basically, i'll plot the this ratio over the other variable.

Here's my array for example:

psi2=[0.6742 0.6784 0.6844 0.6912 0.6975 0.7020 0.7061 0.7122 0.7207 0.7325 0.7486 0.7646 0.7728 0.7715 0.7611 0.7435 0.7262 0.7135 0.7041 0.6972 0.6922 0.6873 0.6819 0.6772 0.6739 0.6728];

and i got energy number

E2=some changing integer

i need the ratio

T=psi2(first5)/psi2(last5)

and plot(T,E2)

Answer 1

[Fabio Freschi]

T = psi2(1:5)./psi(end-4:end);