{"group":{"id":1,"name":"Community","lockable":false,"created_at":"2012-01-18T18:02:15.000Z","updated_at":"2026-05-26T00:16:20.000Z","description":"Problems submitted by members of the MATLAB Central community.","is_default":true,"created_by":161519,"badge_id":null,"featured":false,"trending":false,"solution_count_in_trending_period":0,"trending_last_calculated":"2026-05-26T00:00:00.000Z","image_id":null,"published":true,"community_created":false,"status_id":2,"is_default_group_for_player":false,"deleted_by":null,"deleted_at":null,"restored_by":null,"restored_at":null,"description_opc":null,"description_html":null,"published_at":null},"problems":[{"id":46009,"title":"Pixel density","description":"\u003chttps://en.wikipedia.org/wiki/Pixel_density Pixel density\u003e tells us how many pixels we can find within a unit of length.  And according to the \u003chttps://developer.android.com/guide/topics/resources/providing-resources#AlternativeResources Android developer guide\u003e:\r\n\r\n* Low-density screens have 120 PPI.\r\n* Medium-density screens have 160 PPI.\r\n* High-density screens have 240 PPI. \r\n\r\nA 24\" monitor may have low density if its maximum resolution is small, which means we might lose finer details while gaming or editing images/videos. Given the diagonal of a display in inches, d, and its resolution in pixels, w x h, return its pixel density.","description_html":"\u003cp\u003e\u003ca href = \"https://en.wikipedia.org/wiki/Pixel_density\"\u003ePixel density\u003c/a\u003e tells us how many pixels we can find within a unit of length.  And according to the \u003ca href = \"https://developer.android.com/guide/topics/resources/providing-resources#AlternativeResources\"\u003eAndroid developer guide\u003c/a\u003e:\u003c/p\u003e\u003cul\u003e\u003cli\u003eLow-density screens have 120 PPI.\u003c/li\u003e\u003cli\u003eMedium-density screens have 160 PPI.\u003c/li\u003e\u003cli\u003eHigh-density screens have 240 PPI.\u003c/li\u003e\u003c/ul\u003e\u003cp\u003eA 24\" monitor may have low density if its maximum resolution is small, which means we might lose finer details while gaming or editing images/videos. Given the diagonal of a display in inches, d, and its resolution in pixels, w x h, return its pixel density.\u003c/p\u003e","function_template":"function y = ppi(x)\r\n  y = x;\r\nend","test_suite":"%%\r\nfiletext = fileread('ppi.m');\r\nassert(isempty(strfind(filetext, 'eval')),       'Eval forbidden.');\r\nassert(isempty(strfind(filetext, 'regexp')),     'Regexp forbidden.');\r\nassert(isempty(strfind(filetext, '!')),          'Shell commands are forbidden.');\r\nassert(isempty(strfind(filetext, 'mlock')),      'mlock is forbidden.');\r\nassert(isempty(strfind(filetext, 'munlock')),    'munlock is forbidden.');\r\n%%\r\n% tv screen\r\nd = 40;\r\n% 720p resolution\r\nw = 1280; \r\nh = 720;\r\ny_correct = 36.71;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\n% smartphone\r\nd = 5.5;\r\n% 720p resolution\r\nw = 1280;\r\nh = 720;\r\ny_correct = 267.02;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\n% tablet\r\nd = 7.5;\r\n% 720p resolution\r\nw = 1280;\r\nh = 720;\r\ny_correct = 195.81;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\n% monitor\r\nd = 17;\r\n% 1080p resolution\r\nw = 1920;\r\nh = 1080;\r\ny_correct = 129.58;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 17;\r\n% 2K resolution\r\nw = 2048;\r\nh = 1080;\r\ny_correct = 136.19;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 24;\r\n% UHD resolution\r\nw = 3840;\r\nh = 2160;\r\ny_correct = 183.57;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 24;\r\n% 4K resolution\r\nw = 4096;\r\nh = 2160;\r\ny_correct = 192.94;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 40;\r\n% 8K resolution\r\nw = 7680;\r\nh = 4320;\r\ny_correct = 220.29;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 50;\r\n% 16K resolution \r\nw = 15360;\r\nh = 8640;\r\ny_correct = 352.46;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n","published":true,"deleted":false,"likes_count":0,"comments_count":0,"created_by":443343,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":14,"test_suite_updated_at":"2020-07-01T11:06:44.000Z","rescore_all_solutions":false,"group_id":1,"created_at":"2020-07-01T11:03:22.000Z","updated_at":"2020-07-01T11:06:44.000Z","published_at":"2020-07-01T11:05:32.000Z","restored_at":null,"restored_by":null,"spam":false,"simulink":false,"admin_reviewed":false,"description_opc":"{\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"targetMode\":\"\",\"relationshipId\":\"rId1\",\"target\":\"/matlab/document.xml\"},{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/output\",\"targetMode\":\"\",\"relationshipId\":\"rId2\",\"target\":\"/matlab/output.xml\"}],\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"relationship\":[],\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\\n\u003cw:document xmlns:w=\\\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\\\"\u003e\u003cw:body\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:hyperlink w:docLocation=\\\"https://en.wikipedia.org/wiki/Pixel_density\\\"\u003e\u003cw:r\u003e\u003cw:t\u003ePixel density\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e tells us how many pixels we can find within a unit of length. And according to the\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"https://developer.android.com/guide/topics/resources/providing-resources#AlternativeResources\\\"\u003e\u003cw:r\u003e\u003cw:t\u003eAndroid developer guide\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e:\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"1\\\"/\u003e\u003c/w:numPr\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eLow-density screens have 120 PPI.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"1\\\"/\u003e\u003c/w:numPr\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eMedium-density screens have 160 PPI.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"1\\\"/\u003e\u003c/w:numPr\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eHigh-density screens have 240 PPI.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eA 24\\\" monitor may have low density if its maximum resolution is small, which means we might lose finer details while gaming or editing images/videos. 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And according to the \u003chttps://developer.android.com/guide/topics/resources/providing-resources#AlternativeResources Android developer guide\u003e:\r\n\r\n* Low-density screens have 120 PPI.\r\n* Medium-density screens have 160 PPI.\r\n* High-density screens have 240 PPI. \r\n\r\nA 24\" monitor may have low density if its maximum resolution is small, which means we might lose finer details while gaming or editing images/videos. Given the diagonal of a display in inches, d, and its resolution in pixels, w x h, return its pixel density.","description_html":"\u003cp\u003e\u003ca href = \"https://en.wikipedia.org/wiki/Pixel_density\"\u003ePixel density\u003c/a\u003e tells us how many pixels we can find within a unit of length.  And according to the \u003ca href = \"https://developer.android.com/guide/topics/resources/providing-resources#AlternativeResources\"\u003eAndroid developer guide\u003c/a\u003e:\u003c/p\u003e\u003cul\u003e\u003cli\u003eLow-density screens have 120 PPI.\u003c/li\u003e\u003cli\u003eMedium-density screens have 160 PPI.\u003c/li\u003e\u003cli\u003eHigh-density screens have 240 PPI.\u003c/li\u003e\u003c/ul\u003e\u003cp\u003eA 24\" monitor may have low density if its maximum resolution is small, which means we might lose finer details while gaming or editing images/videos. Given the diagonal of a display in inches, d, and its resolution in pixels, w x h, return its pixel density.\u003c/p\u003e","function_template":"function y = ppi(x)\r\n  y = x;\r\nend","test_suite":"%%\r\nfiletext = fileread('ppi.m');\r\nassert(isempty(strfind(filetext, 'eval')),       'Eval forbidden.');\r\nassert(isempty(strfind(filetext, 'regexp')),     'Regexp forbidden.');\r\nassert(isempty(strfind(filetext, '!')),          'Shell commands are forbidden.');\r\nassert(isempty(strfind(filetext, 'mlock')),      'mlock is forbidden.');\r\nassert(isempty(strfind(filetext, 'munlock')),    'munlock is forbidden.');\r\n%%\r\n% tv screen\r\nd = 40;\r\n% 720p resolution\r\nw = 1280; \r\nh = 720;\r\ny_correct = 36.71;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\n% smartphone\r\nd = 5.5;\r\n% 720p resolution\r\nw = 1280;\r\nh = 720;\r\ny_correct = 267.02;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\n% tablet\r\nd = 7.5;\r\n% 720p resolution\r\nw = 1280;\r\nh = 720;\r\ny_correct = 195.81;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\n% monitor\r\nd = 17;\r\n% 1080p resolution\r\nw = 1920;\r\nh = 1080;\r\ny_correct = 129.58;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 17;\r\n% 2K resolution\r\nw = 2048;\r\nh = 1080;\r\ny_correct = 136.19;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 24;\r\n% UHD resolution\r\nw = 3840;\r\nh = 2160;\r\ny_correct = 183.57;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 24;\r\n% 4K resolution\r\nw = 4096;\r\nh = 2160;\r\ny_correct = 192.94;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 40;\r\n% 8K resolution\r\nw = 7680;\r\nh = 4320;\r\ny_correct = 220.29;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n%%\r\nd = 50;\r\n% 16K resolution \r\nw = 15360;\r\nh = 8640;\r\ny_correct = 352.46;\r\nassert(abs(ppi(d, w, h) - y_correct) \u003c 1e-2);\r\n","published":true,"deleted":false,"likes_count":0,"comments_count":0,"created_by":443343,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":14,"test_suite_updated_at":"2020-07-01T11:06:44.000Z","rescore_all_solutions":false,"group_id":1,"created_at":"2020-07-01T11:03:22.000Z","updated_at":"2020-07-01T11:06:44.000Z","published_at":"2020-07-01T11:05:32.000Z","restored_at":null,"restored_by":null,"spam":false,"simulink":false,"admin_reviewed":false,"description_opc":"{\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"targetMode\":\"\",\"relationshipId\":\"rId1\",\"target\":\"/matlab/document.xml\"},{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/output\",\"targetMode\":\"\",\"relationshipId\":\"rId2\",\"target\":\"/matlab/output.xml\"}],\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"relationship\":[],\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\\n\u003cw:document xmlns:w=\\\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\\\"\u003e\u003cw:body\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:hyperlink w:docLocation=\\\"https://en.wikipedia.org/wiki/Pixel_density\\\"\u003e\u003cw:r\u003e\u003cw:t\u003ePixel density\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e tells us how many pixels we can find within a unit of length. And according to the\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"https://developer.android.com/guide/topics/resources/providing-resources#AlternativeResources\\\"\u003e\u003cw:r\u003e\u003cw:t\u003eAndroid developer guide\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e:\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"1\\\"/\u003e\u003c/w:numPr\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eLow-density screens have 120 PPI.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"1\\\"/\u003e\u003c/w:numPr\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eMedium-density screens have 160 PPI.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"1\\\"/\u003e\u003c/w:numPr\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eHigh-density screens have 240 PPI.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eA 24\\\" monitor may have low density if its maximum resolution is small, which means we might lose finer details while gaming or editing images/videos. 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