# How can weakly/strongly decreasing or increasing approximate sums be explained?

I'm reading around big O to get some concept about performance for data structures. The mathematics book recommended by the open book ~ maths for computer science

In the book (pg 456) part of the pre-requisite knowledge to understand big oh are approximate sums.

I'm struggling to get my head around some of the concepts presented in the book in regards to weakly or strongly decreasing or increasing approximate sums. How exactly can a sum be weak or strong compared to another?

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 I can't seem to find the phrases "weakly approximate sum" or "strongly approximate sum" anywhere in that chapter. Could you be more specific? – Antonio Vargas Feb 26 at 22:22 should be under 13.3 approximating sums :). apologies – peter_gent Feb 26 at 22:29 Are you referring to "weakly decreasing"/"strongly increasing" (etc.) functions? – Antonio Vargas Feb 26 at 23:06 yep I was referring to that. – peter_gent Feb 27 at 13:01 – Cain Mar 1 at 16:41