{"group":{"id":1,"name":"Community","lockable":false,"created_at":"2012-01-18T18:02:15.000Z","updated_at":"2026-09-13T00:11:47.000Z","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":"2026-09-13T00:00:00.000Z","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":1423,"title":"Cos Function","description":"x is the abscissa. find the absolute value of cosine of -x and the same value with changed sign.","description_html":"\u003cdiv style = \"text-align: start; line-height: 20.4333px; min-height: 0px; white-space: normal; color: rgb(0, 0, 0); font-family: Menlo, Monaco, Consolas, monospace; font-style: normal; font-size: 14px; font-weight: 400; text-decoration: rgb(0, 0, 0); white-space: normal; \"\u003e\u003cdiv style=\"block-size: 21px; display: block; min-width: 0px; padding-block-start: 0px; padding-top: 0px; perspective-origin: 407px 10.5px; transform-origin: 407px 10.5px; vertical-align: baseline; \"\u003e\u003cdiv style=\"font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 384px 10.5px; text-align: left; transform-origin: 384px 10.5px; white-space: pre-wrap; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 287.5px 8px; transform-origin: 287.5px 8px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003ex is the input. Find the absolute value of cosine of -x and the same value with opposite sign.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e","function_template":"function [y,z] = cos_abs(x)\r\n  y = x;\r\nend","test_suite":"%%\r\nx = pi;\r\n[y,z] = cos_abs(x)\r\nassert(isequal(y/z,-1))\r\n\r\n\r\n%%\r\nx = pi/2;\r\n[y,z] = cos_abs(x)\r\nassert(abs(y-0)\u003c1e-4)\r\n\r\n\r\n\r\n%%\r\nx = pi/4;\r\n[y,z] = cos_abs(x)\r\nassert(abs(z+1/sqrt(2))\u003c1e-4)\r\n\r\n\r\n%%\r\nx = 0;\r\n[y,z] = cos_abs(x)\r\nassert(isequal(y,1));\r\nassert(isequal(z,-1));","published":true,"deleted":false,"likes_count":1,"comments_count":2,"created_by":3919,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":209,"test_suite_updated_at":"2021-04-19T10:16:35.000Z","rescore_all_solutions":true,"group_id":1,"created_at":"2013-04-12T17:03:43.000Z","updated_at":"2026-04-13T22:17:59.000Z","published_at":"2013-04-12T17:03:43.000Z","restored_at":null,"restored_by":null,"spam":false,"simulink":false,"admin_reviewed":false,"description_opc":"{\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\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\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003ex is the input. Find the absolute value of cosine of -x and the same value with opposite sign.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003c/w:body\u003e\u003c/w:document\u003e\",\"relationship\":null}],\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"target\":\"/matlab/document.xml\",\"relationshipId\":\"rId1\"}]}"},{"id":1508,"title":"Change the sign","description":"Given a matrix x, return one with each diagonal element replaced by its absolute value and the largest element in absolute value *of the off-diagonal elements* in its row...","description_html":"\u003cp\u003eGiven a matrix x, return one with each diagonal element replaced by its absolute value and the largest element in absolute value \u003cb\u003eof the off-diagonal elements\u003c/b\u003e in its row...\u003c/p\u003e","function_template":"function y = SignChange(x)\r\n  y = x;\r\nend","test_suite":"%%\r\nx = [-1 2 3;1 -2 -2;3 3 -3];\r\ny_correct = [ 1 -3 -3;-2 2 -2;-3 -3 3];\r\nassert(isequal(SignChange(x),y_correct))\r\n\r\n%%\r\nx = magic(4);\r\ny_correct = [16 -13 -13 -13; -10 11 -10 -10;-12 -12 6 -12;-15 -15 -15 1];\r\nassert(isequal(SignChange(x),y_correct))\r\n\r\n%%\r\nx = zeros(4);\r\ny_correct = x;\r\nassert(isequal(SignChange(x),y_correct))\r\n\r\n%%\r\nx =  [-1 1 -1;1 -1 1;-1 -2 -3];\r\ny_correct = [1 -1 -1;-1 1 -1;-2 -2 3];\r\nassert(isequal(SignChange(x),y_correct))\r\n","published":true,"deleted":false,"likes_count":1,"comments_count":2,"created_by":810,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":51,"test_suite_updated_at":null,"rescore_all_solutions":false,"group_id":1,"created_at":"2013-05-14T02:24:23.000Z","updated_at":"2026-07-17T16:31:00.000Z","published_at":"2013-05-14T02:26:20.000Z","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:r\u003e\u003cw:t\u003eGiven a matrix x, return one with each diagonal element replaced by its absolute value and the largest element in absolute value\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:rPr\u003e\u003cw:b/\u003e\u003c/w:rPr\u003e\u003cw:t\u003eof the off-diagonal elements\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e in its row...\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003c/w:body\u003e\u003c/w:document\u003e\"},{\"partUri\":\"/matlab/output.xml\",\"contentType\":\"text/xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\" standalone=\\\"no\\\" ?\u003e\u003cembeddedOutputs\u003e\u003cmetaData\u003e\u003cevaluationState\u003emanual\u003c/evaluationState\u003e\u003clayoutState\u003ecode\u003c/layoutState\u003e\u003coutputStatus\u003eready\u003c/outputStatus\u003e\u003c/metaData\u003e\u003coutputArray type=\\\"array\\\"/\u003e\u003cregionArray type=\\\"array\\\"/\u003e\u003c/embeddedOutputs\u003e\"}]}"}],"problem_search":{"problems":[{"id":1423,"title":"Cos Function","description":"x is the abscissa. find the absolute value of cosine of -x and the same value with changed sign.","description_html":"\u003cdiv style = \"text-align: start; line-height: 20.4333px; min-height: 0px; white-space: normal; color: rgb(0, 0, 0); font-family: Menlo, Monaco, Consolas, monospace; font-style: normal; font-size: 14px; font-weight: 400; text-decoration: rgb(0, 0, 0); white-space: normal; \"\u003e\u003cdiv style=\"block-size: 21px; display: block; min-width: 0px; padding-block-start: 0px; padding-top: 0px; perspective-origin: 407px 10.5px; transform-origin: 407px 10.5px; vertical-align: baseline; \"\u003e\u003cdiv style=\"font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 384px 10.5px; text-align: left; transform-origin: 384px 10.5px; white-space: pre-wrap; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 287.5px 8px; transform-origin: 287.5px 8px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003ex is the input. Find the absolute value of cosine of -x and the same value with opposite sign.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e","function_template":"function [y,z] = cos_abs(x)\r\n  y = x;\r\nend","test_suite":"%%\r\nx = pi;\r\n[y,z] = cos_abs(x)\r\nassert(isequal(y/z,-1))\r\n\r\n\r\n%%\r\nx = pi/2;\r\n[y,z] = cos_abs(x)\r\nassert(abs(y-0)\u003c1e-4)\r\n\r\n\r\n\r\n%%\r\nx = pi/4;\r\n[y,z] = cos_abs(x)\r\nassert(abs(z+1/sqrt(2))\u003c1e-4)\r\n\r\n\r\n%%\r\nx = 0;\r\n[y,z] = cos_abs(x)\r\nassert(isequal(y,1));\r\nassert(isequal(z,-1));","published":true,"deleted":false,"likes_count":1,"comments_count":2,"created_by":3919,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":209,"test_suite_updated_at":"2021-04-19T10:16:35.000Z","rescore_all_solutions":true,"group_id":1,"created_at":"2013-04-12T17:03:43.000Z","updated_at":"2026-04-13T22:17:59.000Z","published_at":"2013-04-12T17:03:43.000Z","restored_at":null,"restored_by":null,"spam":false,"simulink":false,"admin_reviewed":false,"description_opc":"{\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\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\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003ex is the input. Find the absolute value of cosine of -x and the same value with opposite sign.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003c/w:body\u003e\u003c/w:document\u003e\",\"relationship\":null}],\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"target\":\"/matlab/document.xml\",\"relationshipId\":\"rId1\"}]}"},{"id":1508,"title":"Change the sign","description":"Given a matrix x, return one with each diagonal element replaced by its absolute value and the largest element in absolute value *of the off-diagonal elements* in its row...","description_html":"\u003cp\u003eGiven a matrix x, return one with each diagonal element replaced by its absolute value and the largest element in absolute value \u003cb\u003eof the off-diagonal elements\u003c/b\u003e in its row...\u003c/p\u003e","function_template":"function y = SignChange(x)\r\n  y = x;\r\nend","test_suite":"%%\r\nx = [-1 2 3;1 -2 -2;3 3 -3];\r\ny_correct = [ 1 -3 -3;-2 2 -2;-3 -3 3];\r\nassert(isequal(SignChange(x),y_correct))\r\n\r\n%%\r\nx = magic(4);\r\ny_correct = [16 -13 -13 -13; -10 11 -10 -10;-12 -12 6 -12;-15 -15 -15 1];\r\nassert(isequal(SignChange(x),y_correct))\r\n\r\n%%\r\nx = zeros(4);\r\ny_correct = x;\r\nassert(isequal(SignChange(x),y_correct))\r\n\r\n%%\r\nx =  [-1 1 -1;1 -1 1;-1 -2 -3];\r\ny_correct = [1 -1 -1;-1 1 -1;-2 -2 3];\r\nassert(isequal(SignChange(x),y_correct))\r\n","published":true,"deleted":false,"likes_count":1,"comments_count":2,"created_by":810,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":51,"test_suite_updated_at":null,"rescore_all_solutions":false,"group_id":1,"created_at":"2013-05-14T02:24:23.000Z","updated_at":"2026-07-17T16:31:00.000Z","published_at":"2013-05-14T02:26:20.000Z","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:r\u003e\u003cw:t\u003eGiven a matrix x, return one with each diagonal element replaced by its absolute value and the largest element in absolute value\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:rPr\u003e\u003cw:b/\u003e\u003c/w:rPr\u003e\u003cw:t\u003eof the off-diagonal elements\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e in its row...\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003c/w:body\u003e\u003c/w:document\u003e\"},{\"partUri\":\"/matlab/output.xml\",\"contentType\":\"text/xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\" standalone=\\\"no\\\" ?\u003e\u003cembeddedOutputs\u003e\u003cmetaData\u003e\u003cevaluationState\u003emanual\u003c/evaluationState\u003e\u003clayoutState\u003ecode\u003c/layoutState\u003e\u003coutputStatus\u003eready\u003c/outputStatus\u003e\u003c/metaData\u003e\u003coutputArray type=\\\"array\\\"/\u003e\u003cregionArray type=\\\"array\\\"/\u003e\u003c/embeddedOutputs\u003e\"}]}"}],"errors":[],"facets":[[],[{"value":"easy","count":1,"selected":false},{"value":"medium","count":1,"selected":false}]],"term":"tag:\"change sign\"","page":1,"per_page":50,"sort":"map(difficulty_value,0,0,999) asc"}}