Neglect terms of order $1/n$ - Mathematica Stack Exchange most recent 30 from mathematica.stackexchange.com 2019-09-22T04:54:14Z https://mathematica.stackexchange.com/feeds/question/191313 https://creativecommons.org/licenses/by-sa/4.0/rdf https://mathematica.stackexchange.com/q/191313 0 Neglect terms of order $1/n$ Bounded https://mathematica.stackexchange.com/users/58940 2019-02-11T15:49:00Z 2019-02-11T15:58:20Z <p>I have expressions like the following <span class="math-container">$A+B/n+C/n^2+\cdots,Z/n^p$</span>. I'd like to keep just the first two terms, i.e., <span class="math-container">$A+B/n,$</span> however it seems that using the command O[1/n^2] is not working. The O[] command used to neglect higher-order terms seems to work only for expressions like <span class="math-container">$$A+B n+C n^2+\cdots,Z n^p.$$</span> Is there any workaround to deal with expressions like mine?</p> https://mathematica.stackexchange.com/questions/191313/neglect-terms-of-order-1-n/191315#191315 5 Answer by Carl Woll for Neglect terms of order $1/n$ Carl Woll https://mathematica.stackexchange.com/users/45431 2019-02-11T15:58:20Z 2019-02-11T15:58:20Z <p>Given:</p> <pre><code>expr = a + b/n + c/n^2 + d/n^3; </code></pre> <p>Use either:</p> <pre><code>expr + O[n, Infinity]^2 //TeXForm </code></pre> <blockquote> <p><span class="math-container">$a+\frac{b}{n}+O\left(\left(\frac{1}{n}\right)^2\right)$</span></p> </blockquote> <p>or:</p> <pre><code>Series[expr, {n, Infinity, 1}] //TeXForm </code></pre> <blockquote> <p><span class="math-container">$a+\frac{b}{n}+O\left(\left(\frac{1}{n}\right)^2\right)$</span></p> </blockquote>