{"id":1542,"date":"2017-11-20T21:35:24","date_gmt":"2017-11-21T02:35:24","guid":{"rendered":"http:\/\/blog.richmond.edu\/math320\/?p=1542"},"modified":"2017-11-26T12:34:07","modified_gmt":"2017-11-26T17:34:07","slug":"muddiest-point-1116","status":"publish","type":"post","link":"https:\/\/blog.richmond.edu\/math320\/2017\/11\/20\/muddiest-point-1116\/","title":{"rendered":"Muddiest Point 11\/16"},"content":{"rendered":"<p>In this edition of the muddiest point I will go over non-Riemann integrable functions. Let&#8217;s review a classic example that we mentioned in class, the Dirichlet function. Define the Dirichlet Function as<br \/>\n$<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f%28x%29%3D%5Cbegin%7Bcases%7D+1%5C+%5Ctext%7Bif%7D%5C+x%5Cin%5Cmathbb%7BQ%7D%5C%5C++0%5C+%5Ctext%7Bif%7D%5C+x%5Cnotin%5Cmathbb%7BQ%7D%5Cend%7Bcases%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f(x)=&#92;begin{cases} 1&#92; &#92;text{if}&#92; x&#92;in&#92;mathbb{Q}&#92;&#92; 0&#92; &#92;text{if}&#92; x&#92;notin&#92;mathbb{Q}&#92;end{cases}\" class=\"latex\" \/>$<br \/>\nRecall that by definition, A bounded function <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f\" class=\"latex\" \/> defined on the interval <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Ba%2Cb%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"[a,b]\" class=\"latex\" \/> is Riemann-integrable if <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=U%28f%29%3DL%28f%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"U(f)=L(f)\" class=\"latex\" \/>. For <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cmathbb%7BP%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;mathbb{P}\" class=\"latex\" \/>, the set of all possible partitions of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Ba%2Cb%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"[a,b]\" class=\"latex\" \/>, we call <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=U%28f%29%3D%5Cinf%5C%7BU%28f%2CP%29%3AP%5Cin%5Cmathbb%7BP%7D%5C%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"U(f)=&#92;inf&#92;{U(f,P):P&#92;in&#92;mathbb{P}&#92;}\" class=\"latex\" \/> the upper integral of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f\" class=\"latex\" \/>. Similarly, <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=L%28f%29%3D%5Csup%5C%7BL%28f%2CP%29%3AP%5Cin%5Cmathbb%7BP%7D%5C%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"L(f)=&#92;sup&#92;{L(f,P):P&#92;in&#92;mathbb{P}&#92;}\" class=\"latex\" \/> is the lower integral of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f\" class=\"latex\" \/>. (Notice that these use the lower and upper sums that we discussed in class. We define the lower sum <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=L%28f%2CP%29%3D%5Csum_%7Bk%3D1%7D%5En+m_k%28x_k-x_%7Bk-1%7D%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"L(f,P)=&#92;sum_{k=1}^n m_k(x_k-x_{k-1})\" class=\"latex\" \/> and the upper sum <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=U%28f%2CP%29%3D%5Csum_%7Bk%3D1%7D%5En+M_k%28x_k-x_%7Bk-1%7D%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"U(f,P)=&#92;sum_{k=1}^n M_k(x_k-x_{k-1})\" class=\"latex\" \/>).<\/p>\n<p>Well, looking at the Dirichlet function, we can see that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=U%28f%29%3D1&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"U(f)=1\" class=\"latex\" \/>, but <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=L%28f%29%3D0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"L(f)=0\" class=\"latex\" \/>. It follows that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=1%5Cneq+0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"1&#92;neq 0\" class=\"latex\" \/>, so the function is not Reimann integrable. This way of showing that the upper and lower integrals of a functions are not equal will most likely be one of our main tools to show that a function is not Riemann integrable.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>In this edition of the muddiest point I will go over non-Riemann integrable functions. Let&#8217;s review a classic example that we mentioned in class, the Dirichlet function. Define the Dirichlet Function as $$ Recall that by definition, A bounded function defined on the interval is Riemann-integrable if . For , the set of all possible [&hellip;]<\/p>\n","protected":false},"author":3526,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[58822],"tags":[],"class_list":["post-1542","post","type-post","status-publish","format-standard","hentry","category-muddiest-point"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p7L4E1-oS","jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts\/1542","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/users\/3526"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/comments?post=1542"}],"version-history":[{"count":0,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts\/1542\/revisions"}],"wp:attachment":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/media?parent=1542"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/categories?post=1542"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/tags?post=1542"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}