23 2323 23152010-02-12 15:22:44 / rev 1ea03ec8b94a+importscarsN3 × 108miles/year104gallons/mile1/25barrels/gallon1/40other uses2fraction imported0.5All the leaves have values, so I can propagate upward to the root. Themain operation is multiplication. For the ‘cars’ node:3×108cars×104miles1 car–year×1 gallon25 miles×1 barrel40 gallons∼ 3×109barrels/year.The two adjustment leaves contribute a factor of 2 ×0.5 = 1, so the importestimate is3 × 109barrels/year.For 2006, the true value (from the US Dept of Energy) is 3.7×109barrels/year– only 25 higher than the estimate!Problem 1.5 MidpointsThe midpoint on the log scale is also known as the geometric mean. Show thatit is never greater than the midpoint on the usual scale (which is also known asthe arithmetic mean). Can the two midpoints ever be equal?1.5 Example 4: The UNIX philosophyThe preceding examples illustrate how divide and conquer enables accu-rate estimates. An example remote from estimation – the design principlesof the UNIX operating system – illustrates the generality of this tool.UNIX and its close cousins such as GNU/Linux operate devices as smallas cellular telephones and as large as supercomputers cooled by liquidnitrogen. They constitute the world’s most portable operating system.Its success derives not from marketing – the most successful variant,GNU/Linux, is free software and owned by no corporation – but ratherfrom outstanding design principles.These principles are the subject of The UNIX Philosophy [13], a valuablebook for anyone interested in how to design large systems. The author23 2323 23152010-02-12 15:22:44 / rev 1ea03ec8b94a+importscarsN3 × 108miles/year104gallons/mile1/25barrels/gallon1/40other uses2fraction imported0.5All the leaves have values, so I can propagate upward to the root. Themain operation is multiplication. For the ‘cars’ node:3×108cars×104miles1 car–year×1 gallon25 miles×1 barrel40 gallons∼ 3×109barrels/year.The two adjustment leaves contribute a factor of 2 ×0.5 = 1, so the importestimate is3 × 109barrels/year.For 2006, the true value (from the US Dept of Energy) is 3.7×109barrels/year– only 25 higher than the estimate!Problem 1.5 MidpointsThe midpoint on the log scale is also known as the geometric mean. Show thatit is never greater than the midpoint on the usual scale (which is also known asthe arithmetic mean). Can the two midpoints ever be equal?1.5 Example 4: The UNIX philosophyThe preceding examples illustrate how divide and conquer enables accu-rate estimates. An example remote from estimation – the design principlesof the UNIX operating system – illustrates the generality of this tool.UNIX and its close cousins such as GNU/Linux operate devices as smallas cellular telephones and as large as supercomputers cooled by liquidnitrogen. They constitute the world’s most portable operating system.Its success derives not from marketing – the most successful variant,GNU/Linux, is free software and owned by no corporation – but ratherfrom outstanding design principles.These principles are the subject of The UNIX Philosophy [13], a valuablebook for anyone interested in how to design large systems. The authorGlobal comments 1Global commentsI’m having a hard time reading this section (I have no background really in coding, nordo I use UNIX). I feel like I’m going to have to read this a bunch of times before I beginto understand what is actually going on. I understand the use of divide in conquer in thiscontext, I’m just mostly confused following these examples (considering how easy andgreat the previous sections were to read).I agree with this. There is so much technical jargon in this section that most of my timeis spent trying to understand and remember the new terms/commands instead of divideand conquer.Agreed - I suggested there be a short description of how UNIX works preceding thischapter. I don’t have much UNIX experience either and was quite confused, so Iimagine everyone else in the same boat would have similar problems.I feel the exact same way....divide and conquer permeates all of this section, but that’sthe extent of my understanding.I agree with previous comments; it would also be helpful if you defined or explained someof the terms being used in this section – utility, input/output, like you did for "filter"was UNIX the first program with this kind of search function (ie. searching for trivial,nontrivial, trivializes along with trivial)? This seems to be pretty ubiquitous with allsearches nowadays.Wikipedia says that there was earlier precedents. But UNIX seems to be the firstsystem to use regular expressions everywhere. A nice feature of the UNIX approachis that the grep program gives you back lines, on which you can do more things (likein class when we extracted the email addresses from the Stellar HTML file).This section requires a foundational knowledge of UNIX that I don’t think most peoplehave...the overall message of divide and conquer is being lost amongst all these functionsthat are being used.I agree to a certain extent. While I’m familiar with Unix, I could imagine this sectiondiscouraging those who do not. Is it possible to illustrate the concepts another way?23 2323 23152010-02-12 15:22:44 / rev 1ea03ec8b94a+importscarsN3 × 108miles/year104gallons/mile1/25barrels/gallon1/40other uses2fraction imported0.5All the leaves have values, so I can propagate upward to the root. Themain operation is multiplication. For the ‘cars’ node:3×108cars×104miles1 car–year×1 gallon25 miles×1 barrel40 gallons∼ 3×109barrels/year.The two adjustment leaves contribute a factor of 2 ×0.5 = 1, so the importestimate is3 × 109barrels/year.For 2006, the true value (from the US Dept of Energy) is 3.7×109barrels/year– only 25 higher than the estimate!Problem 1.5 MidpointsThe midpoint on the log scale is also known as the geometric mean. Show thatit is never greater than the midpoint on the usual scale (which is also known asthe arithmetic mean). Can the two midpoints ever be equal?1.5 Example 4: The UNIX philosophyThe preceding examples illustrate how divide and conquer enables accu-rate estimates. An example remote from estimation – the design principlesof the UNIX operating system – illustrates the generality of this tool.UNIX and its close cousins such as GNU/Linux operate devices as smallas cellular telephones and as large as supercomputers cooled by liquidnitrogen. They constitute the world’s