// Numbas version: exam_results_page_options
{"name": "Graph solution", "extensions": ["jsxgraph"], "custom_part_types": [], "resources": [], "navigation": {"allowregen": true, "showfrontpage": false, "preventleave": false, "typeendtoleave": false}, "question_groups": [{"pickingStrategy": "all-ordered", "questions": [{"functions": {}, "ungrouped_variables": ["a", "c"], "name": "Graph solution", "tags": ["jsxgraph", "Jsxgraph", "plot", "quadratic"], "advice": "", "rulesets": {"std": ["all", "fractionNumbers"]}, "parts": [{"prompt": "<p>The graph of this formula is:</p>", "matrix": ["if(a>0,1,0)", "if(a>0,0,1)"], "shuffleChoices": false, "marks": 0, "variableReplacements": [], "choices": ["<p>An upwards-opening parabola</p>", "<p>A downwards-opening parabola</p>"], "variableReplacementStrategy": "originalfirst", "displayType": "radiogroup", "maxMarks": 1, "scripts": {}, "distractors": ["", ""], "displayColumns": 0, "showCorrectAnswer": true, "type": "1_n_2", "minMarks": 0}], "statement": "<p>Drag the points on the graph to sketch the formula y = $x^2 + 4x + 2$</p>", "variable_groups": [], "variablesTest": {"maxRuns": 100, "condition": ""}, "preamble": {"css": "table#values th {\n  background: none;\n  text-align: center;\n}", "js": "function dragpoint_board() {\n  var scope = question.scope;\n  \n  var a = scope.variables.a.value;\n  var c = scope.variables.c.value;\n  var maxy = Math.max(Math.abs(a*9+c),Math.abs(c));\n  \n  var div = Numbas.extensions.jsxgraph.makeBoard('250px','400px',{boundingBox:[-5,maxy+3,5,-maxy-3],grid:true});\n  $(question.display.html).find('#dragpoint').append(div);\n  \n  var board = div.board;\n  \n  //shorthand to evaluate a mathematical expression to a number\n  function evaluate(expression) {\n    try {\n      var val = Numbas.jme.evaluate(expression,question.scope);\n      return Numbas.jme.unwrapValue(val);\n    }\n    catch(e) {\n      // if there's an error, return no number\n      return NaN;\n    }\n  }\n  \n  // set up points array\n  var num_points = 7;\n  var points = [];\n  \n  \n  // this function sets up the i^th point\n  function make_point(i) {\n    \n    // calculate initial coordinates\n    var x = i-(num_points-1)/2;\n    \n    // create an invisible vertical line for the point to slide along\n    var line = board.create('line',[[x,0],[x,1]],{visible: false});\n    \n    // create the point\n    var point = points[i] = board.create(\n      'glider',\n      [i-(num_points-1)/2,0,line],\n      {\n        name:'',\n        size:2,\n        snapSizeY: 0.1,  // the point will snap to y-coordinates which are multiples of 0.1\n        snapToGrid: true\n      }\n    );\n    \n    // the contents of the input box for this point\n    var studentAnswer = question.parts[1].gaps[i].display.studentAnswer;\n    \n    // watch the student's input and reposition the point when it changes.    \n    ko.computed(function() {\n      y = evaluate(studentAnswer());\n      if(!(isNaN(y)) && board.mode!=board.BOARD_MODE_DRAG) {\n        point.moveTo([x,y],100);\n      }\n    });\n    \n    // when the student drags the point, update the gapfill input\n    point.on('drag',function(){\n      var y = Numbas.math.niceNumber(point.Y());\n      studentAnswer(y);\n    });\n    \n  }\n  \n  // create each point\n  for(var i=0;i<num_points;i++) {\n    make_point(i);\n  }\n  \n  // create the parabola\n  var parabool = board.create('spline',points,{strokeWidth:3,strokeColor:'red'});\n}\n\nquestion.signals.on('HTMLAttached',function() {\n  dragpoint_board();\n}); "}, "variables": {"a": {"definition": "random(-2,-1,-0.5,0.5,1,2)", "templateType": "anything", "group": "Ungrouped variables", "name": "a", "description": ""}, "c": {"definition": "random(-4..4 except 0)", "templateType": "anything", "group": "Ungrouped variables", "name": "c", "description": ""}}, "metadata": {"notes": "<p>function adapted from a question written in Dutch by Carolijn Tacken.</p>", "description": "<p>Drag points on a&nbsp;JSXgraph plot&nbsp;to sketch solution</p>", "licence": "Creative Commons Attribution 4.0 International"}, "type": "question", "showQuestionGroupNames": false, "question_groups": [{"name": "", "pickingStrategy": "all-ordered", "pickQuestions": 0, "questions": []}], "contributors": [{"name": "Phil Barker", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/624/"}]}]}], "contributors": [{"name": "Phil Barker", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/624/"}]}