DiscussionTelling a computer how to behave ( via pseudocode, a workaround for Computing’s Tower of Babel.)Recall: ScribblerRecall: Scribbler’s “Language”Scribbler language illustrates essential features of all computer languagesFor a computer, everything’s a numberA simple problemSolutionSimilar question in different setting Memory: a simplified viewExamplesArraysProcedure findminAnother way to express the same procedure.New problem for robot: sortingSolutionSwappingAlgorithmDiscussion Did last week’s lectures and the assigned reading from “Flesh and Machines” make you look at things around you in a new way? How would you summarize Brooks’ key insights that led him to design Genghis?Telling a computer how to behave( via pseudocode, a workaround for Computing’s Tower of Babel.)2/14/2006COS 116Instructor: Sanjeev AroraFace valueSt Lawrence of GoogleJan 12th 2006Paul Saffo at Silicon Valley's Institute for the Future says that “Google is a religion posing as a company.”Playing GodIf Google is a religion, what is its God?It would have to be The Algorithm.Recall: ScribblerLight outputsSpeakerLight sensorsObstacle sensor emitterObstacle sensor detectorStall sensorLine sensor (underneath)Motor/wheelsInputs OutputsRecall: Scribbler’s “Language” Several types of simple instructions E.g. “Move forward for 1 s” Two types of compound instructionsIf <condition> Then{List of instructions}Else{List of instructions}Do for i = 1 to x{List of instructions}Conditional (a.k.a. Branching)LoopScribbler language illustrates essential features of all computer languages Fundamental features of human languages:nouns/verbs/adjectives, subjects/objects, pronouns, etc. Computer languages also share fundamental features, e.g. conditional and loop statements, variables, ability to perform arithmetic, etc.JavaC++BASICPythonComputing’s Tower of BabelFor a computer, everything’s a numberAudio waveformSequence of Numbers representing frequency, amplitude, etc.Sequence of Numbers representing red/green/blue color value of each pixel.ImageA simple problem Say your robot is getting ready for a big date… How would a robot identify the cheapest bottle? (Say it can scan prices)Solution Pick up first bottle, check price Walk down aisle, for each bottle, do the following: If price on bottle < price on bottle in hand, put down the one in you hand and pick up the new bottleSimilar question in different setting Suppose robot has n prices stored in memory Want to find minimum priceMemory: a simplified view A scratchpad that can be perfectly erased and re-written any number of times A variable: a piece of memory with a name; stores a “value”Examplesi ← 5i ← ji ← j + 1Sets i to value 5Sets i to whatever value is in j; leaves j unchangedSets i to j + 1; leaves junchangedArrays A is an array of n values, A[ i ] is the i’thvalue Example: A[3] = 52.9940.99 62.99 52.99…22.99A =Procedure findmin n items, stored in array A Variables are i, best best ← 1 Do for i = 2 to n{if (A[ i ] < A[best]) then{ best ← i }}Another way to express the same procedure.best ← 1;i ← 2Do while (i <= n){if (A[ i ] < A[best]) then{ best ← i }i ← i + 1;}New problem for robot: sortingArrange them so prices increase from left to right.SolutionDo for i=1 to n-1{Find cheapest bottle among those numbered i to nSwap that bottle and the i’th bottle.}“selection sort”Swapping Suppose x and y are variables. How do you swap their values? Need extra variable!tmp ← xx ← yy ← tmpAlgorithm A precise unambiguous procedure for accomplishing a task Named for Abu Abdullah Muhammad bin Musa al-Khwarizmi For example, addition, long division, selection
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