How do I fprintf a title for every third iteration in a loop?

This is the output I have to achieve. I'm able to get the reactions but I don't know how to get the Reaction sub mechanism: # title for every third reaction and the matrix shown after every third reaction. I screenshotted the output starting at sub reaction 7 because the first 6 sub reactions began with r1 which could be solved with an if statement within the loop like I initially did. The sub reactions go from 1-15.

 Thanks for the help!

Answer 1

[Jos (10584)]

In pseudocode it would look like this:

if mod(linecounter,3)==0
   print header
end
print line
linecounter = linecounter + 1